In Tattoo, Deucalion, Kali, and Ennis arrived at Beacon Hills Memorial Hospital in search for Derek Hale's Beta, Isaac Lahey, and Braeden, the mercenary who was hired to save him. In the hospital elevator, he came into contact with Scott McCall, who he asked to press the button for the second floor for him due to his lack of eyesight.
When Scott did so, Deucalion thanked him, and once they arrived on their floor, he asked Scott if he could help him get out of the elevator, which he did, albeit reluctantly. Later that day, at Beacon Hills High School Deucalion, along with the rest of the Alpha Pack, tracked Braeden to the boys locker room, where she fended off Ennis, Ethan, and Aiden with nothing but her body and a broken mop handle before she was subdued by Kali.
Afterward, Deucalion approached her, remarking on the fact that Braeden is both beautiful and defiant, to which she retorted that she knew he was afraid of Scott, and specifically the man Scott would become as a True Alpha. This led Deucalion to concede that, while he was aware of the potential threat that Scott posed to his pack, he was taking the advice of "someone" who said that the best way to eliminate threats was to get someone else to do it for them. Braeden realized that Deucalion was implying that he would manipulate Derek into killing Scott for him, which caused Deucalion to rear his arm backward and slash her across the throat with his claws.
Meanwhile, at the Hale House ruins, Scott and Stiles Stilinski confronted Derek, who was forced to confess that the Alpha Pack had been in Beacon Hills for almost four months, and that they abducted Erica Reyes and Vernon Boyd, who Derek, Isaac, and Peter Hale had been searching for all this time. Derek also informed Scott and Stiles that Deucalion was the leader of his pack.
In Chaos Rising, it was revealed that Deucalion and the other Alphas killed Erica Reyes and captured Boyd and Cora Hale when Alan Deaton helped Scott, Stiles, and Derek perform a memory retrieval ritual for Isaac to try to regain the memories the Alphas stole from him when they attacked him.
Just as Derek and Scott had arrived at the First National Bank after they had figured out Boyd and Erica were being held captive there, Stiles and Peter called them to inform them that the bank vault was lined with hecatolite (also known as moonstone), which scatters moonlight and had prevented the Werewolf captives from transforming for the last four months, therefore diminishing their resistance to the sway of the moon-- as a result, that night's full moon would turn them into vicious, feral beasts who are incapable of controlling themselves. Before the two could react further, Deucalion's Emissary, Marin Morrell, completed the Mountain Ash barrier around the vault at his request, trapping Derek, Scott, Boyd, and Cora in hopes that Derek, Scott, or both would kill the other two in order to pave their way into joining the Alpha Pack's ranks.
In Fireflies, Deucalion was mentioned in a conversation between Derek and Peter Hale when the latter informed Derek that Deucalion had captured Boyd and Cora and kept them from shifting for three months so that Derek would have no choice but to kill them, which would then cause Derek to take the first steps in joining the Alpha Pack (i.e. killing his Betas and stealing their power) just as Deucalion wanted. However, this revelation only made Derek more determined to keep Boyd and Cora alive to prevent Deucalion from getting what he wanted, and he was nearly mauled to death in the process of doing so.
In Unleashed, Deucalion, along with Kali and Ennis broke into Derek's loft to have a discussion with him. After Kali defeated Derek and Ennis easily took down Cora, Deucalion entered the loft, humorously remarking that the violence sounded "exhausting" before stating his desire to discuss a plan with Derek about their future together.
Derek assumed that Deucalion wanted to kill him, but Deucalion was insulted by this, scoffing that Derek would categorize him with "common sociopaths" like his uncle, Peter Hale. Deucalion went on to say that he has always been on the lookout for new talent, and he saw this potential in Derek, offering the younger Alpha a place in the Alpha Pack. Derek immediately refused the offer, as he knew that Deucalion wanted him to kill his own Betas, but Deucalion assured him that he only wanted Derek to kill one of them, believing that once he had done that, he would happily kill the others of his own volition.
Deucalion then proceeded to tell the story of how he killed his first Beta, Marco; according to him, after he lost his eyesight, his Beta decided he was no longer fit for his role as Alpha and challenged Deucalion. Deucalion ultimately won this battle, but he learned after killing him that when an Alpha kills his own Beta, they absorbed their power and thus became more powerful themselves. This realization led Deucalion to kill the rest of his Betas as well, which resulted in him becoming stronger, faster, and generally more powerful than he had ever been. Deucalion explained that this became the origin of the Alpha Pack, as Kali and Ennis also killed their Betas and Emissary as initiation into his new pack.
After asking Kali how it felt to take the power of her own, Kali smirked that it was "liberating," which supported Deucalion's argument that Derek was outgrowing his role as "Alpha to a couple of maladjusted teenagers" and that they would soon become a liability, even suggesting that he knew one of his Betas was in trouble as they spoke. Deucalion then began touching Derek's face, eventually agreeing with Kali that Derek looked like his mother, Talia Hale, revealing that they were acquainted.
However, Derek was not convinced by Deucalion's pitch and stated that he was a fanatic, leading Deucalion to dramatically declare that he was much more than that. His voice became deeper and more powerful as he ranted the following: "I am the Alpha of Alphas. I am the apex of apex predators. I am Death, Destroyer of Worlds! I am the Demon Wolf!" This declaration was paired with cracks of thunder and lightning, and his voice became so loud that he shattered the lenses of his sunglasses. After this point, Deucalion and his compatriots left Derek's loft, with Derek aware that all of his Betas were in danger.
Afterward, Deucalion appeared at the high school, where he intervened in a fight between Scott McCall, Isaac Lahey, and his packmates Ethan and Aiden Steiner. After roaring at them to stop, Deucalion punished them by swiping them both across the cheek with the blade concealed at the end of his cane before he forced the twins to leave with him. It was then that Isaac and Scott realized that the man was Deucalion, the leader of the Alpha Pack.
In Frayed, Deucalion entered the elevator in the building where the Argent Apartment was located just as Scott McCall was leaving from warning Allison Argent about the threat of the Alpha Pack. Scott wasted no time extending his claws, but Deucalion merely chuckled and stated that he would have to be blind, deaf, and paraplegic for Scott to be any threat to him.
After further consideration, Deucalion suggested that Scott may be able to rise to the occasion, as he could hear Scott's heartbeat and could tell that, while he was afraid, he was controlling it. Scott argued that he wasn't like Deucalion because he didn't kill people, Deucalion cryptically replied that he would eventually find that at some point, he might have to choose between killing someone or having someone he cared about die. Scott assumed that Deucalion came all the way to the Argents' apartment building just to threaten him, but Deucalion revealed that he actually lived in the building and that his neighbors were surprisingly friendly. Just then, the elevator reached the ground floor, and Scott watched in concern as Deucalion asked one of the people entering the elevator if they could press the button for the penthouse.
Once Scott learned that the Hale Pack intended to ambush Deucalion and take him out, assuming that by doing so, the Alpha Pack would fall apart without him, he once again contacted Deucalion to set up a meeting where they could possibly come to a truce. They agreed to meet at an abandoned mall in Beacon Hills, and despite Scott's best efforts, he was unable to talk his friend and foster brother Isaac Lahey from accompanying him there.
Unfortunately, it was revealed upon their arrival that Derek Hale had intended for Scott to do just this to give them the opportunity to get Deucalion alone. However, Deucalion was aware of what was about to occur and made sure to bring his pack with him, leading to an all-out brawl between the members of each pack: Derek, Cora Hale, Vernon Boyd, and a reluctant Scott and Isaac against Kali, Ennis, and Ethan and Aiden, while Deucalion sat out and sensed the fight around him. Despite the Hale Pack and their ally's best efforts, the Alpha Pack ultimately overpowered them, giving Deucalion the opportunity to make Derek a deal-- if he killed Boyd, then the others could leave with their lives.
When Kali protested against all of the trouble they were going through to get Derek, who she believed was simply an Alpha to a group of "loser teenagers," Deucalion retorted that some of them had more promise than others, implying that Scott was yet another member he had his eye on. Kali insisted that Derek rise to the occasion and changed the ultimatum, giving him the choice between killing his Beta Boyd or his sister Cora. Fortunately for them, Allison Argent appeared just before he had to act, using her flash-bang arrows to disorient and temporarily blind the Alphas so that the Hale Pack could get the upper hand once again. Deucalion, triggered by the memory of being blinded, urged all in attendance to protect their eyes as she shot arrow after arrow.
The fight broke out again in earnest, with Scott, Isaac, and Derek still fighting the Alphas while Cora got the severely-injured Boyd out of the way. The battle was more balanced the second time around, and just as Scott was about to help Derek defeat Ennis by clawing out his Achilles tendon, Ennis fell over the edge of the construction area and pulled Derek down with him, presumably killing them both and causing the rest of the Werewolves to scatter.
In Motel California, Deucalion was summoned to the Beacon Hills Animal Clinic, where Kali and Aiden (led by their Emissary Marin Morrell, the sister of the owner) had brought the gravely injured Ennis for treatment by Alan Deaton. Deaton was initially refusing to help them, but once Morrell reminded Deaton that his protégée Scott McCall would become a target of the Alpha Pack if Ennis died, leading the veterinarian and Druid to reluctantly agree to help.
Once Ennis had been stabilized, Deucalion came to check in on him, seemingly pleased by the report that Ennis would survive his injuries. Deaton was then appalled to see Deucalion kill Ennis with his bare hands by squeezing his skull until it shattered, making it clear that Deucalion intended to use Ennis' death to make the Alphas put more pressure on Derek and Scott.
Meanwhile, Scott and his comrades were at the Glen Capri Motel as part of a cross-country meet for the high school, along with Alpha Pack member Ethan Steiner. The Werewolves in attendance were exposed to purple wolfsbane and began experiencing terrifying hallucinations; Scott, specifically, hallucinated that Deucalion had come to the motel with his mother Melissa McCall as a hostage, where he slit her throat with his claws in the parking lot while Scott watched. This caused Scott so much despair that he nearly committed suicide by dousing himself in gasoline and lighting himself on fire with a flare.
On their way back to Beacon Hills, Ethan, grateful to Scott for his "pack's" assistance in saving his life while hallucinating, warned Scott that since Derek had allegedly killed Ennis, Kali would be coming for him, and he would have to either kill his pack (including Scott and his friends) and join them, or Kali would kill them all.
In Currents, after Danny Mahealani was rushed to the hospital with mistletoe poisoning, Scott immediately blamed Deucalion and the rest of the Alpha Pack. However, Ethan assured him that they had nothing to do with it, and Scott pointed out that all he knew was that Ethan made a bee-line for Danny as soon as the Alphas showed up, and his twin Aiden did the same with Lydia, which made it seem as though they were targeting the two. Ethan argued that Deucalion and the rest of the Alphas knew that one of them was going to be important to Scott, and they eventually figured out that it was Lydia.
Meanwhile, the alarms went off at Derek's loft, causing Derek and Cora to realize that the Alpha Pack's symbol had been spray-painted on the wall of windows in the back of the apartment. When Cora questioned what the symbol meant, Derek explained that the Alpha Pack was warning him that they were coming to fight him this next evening.
When Alan Deaton was captured by the Darach as one of her healer sacrifices, the McCall Pack's members all split off to follow various leads in hopes of finding him before he was killed. Scott was about to head to the Argent Apartment at Allison's request to learn what she had discovered when he suddenly heard a rhythmic tapping noise that lured him into the band room, where he found Deucalion waiting for him.
Deucalion was impressed with Scott's ability to control his emotions, noting that he could tell that his heart was pounding, but not out of fear-- out of anger. When Scott continued to glare at him, Deucalion guessed that Scott thought he had something to do with Deaton's disappearance and made him an offer-- if Scott could snatch Deucalion's cane out of his hands, then he would tell Scott where Deaton was being held captive. Scott wasted no time agreeing to the challenge and put in his best effort, managing to evade Deucalion's strikes but unable to make an offensive move. Finally, the fight ended when Deucalion stabbed Scott in the shoulder with the blade hidden at the end of his cane, but the Alpha conceded that Scott's efforts were still impressive.
Deucalion then returned to the topic at hand by saying "But, you know I'm not the one slashing up innocent people, praying to ancient gods, gathering herbs, or whatever the hell Druids are supposed to do." He went on to remind Scott that he was a part of a pack that was eager to see Derek dead and revealed that Kali would be going after him, referencing the symbol tagged on Derek's windows.
Deucalion wrapped up their conversation by informing Scott that he was about to be forced to make a difficult decision-- someone was going to die that night, either Derek or Deaton, and it was up to Scott to decide who would survive. Scott, certain that he would be able to save them both, demanded to know where Deaton was being held, but since he didn't win the challenge, Deucalion would only give him a clue: "Let the current guide you."
After a great deal of work figuring out where Deaton was hidden, Scott ultimately sent the others to the loft to help Derek survive his battle with Kali while he went to get Deaton himself. Unfortunately for Scott, Deaton was being suspended from the ceiling bound at the wrists and was slowly suffocating while surrounded by a barrier of Mountain Ash. Desperate, Scott began pushing against the barrier as hard as he could in hopes of breaking it, and the effort of doing so took so much energy that Scott's eyes briefly flashed from Beta gold to Alpha red.
Though Scott wasn't able to break through the barrier, Sheriff Stilinski arrived just in time to free Deaton himself, and when Scott and Deaton were alone, Deaton excitedly informed him that his eyes had turned red and that this meant he was a True Alpha, or an Alpha who doesn't have to kill or steal power because they ascend to the status out of sheer force of will. Scott was shocked by this news, and Deaton insisted that he had a feeling Scott would be a True Alpha from the moment he was first bitten. This caused Scott to realize that Deucalion also knew this fact, and Deaton grimly confirmed his suspicions by revealing that Deucalion wasn't truly in Beacon Hills to recruit Derek, he was there to recruit Scott.
In Visionary, Deucalion was seen exclusively in flashbacks to events in the early 2000s as two connected stories were told by Gerard Argent (to Scott McCall and Allison Argent) and Peter Hale (to Stiles Stilinski and Cora Hale).
Before the stories were told, Scott and Allison confronted Gerard at his nursing home and demanded to know how they could beat Deucalion. Gerard refused without Scott first taking some of his pain, but afterward, Gerard grimly stated that Deucalion couldn't be beaten, because he already tried. After Allison tricked him into telling the truth by making him feel useless, Gerard admitted, "I can tell you one thing-- Deucalion may have lost his eyes, but he's not always blind."
Gerard then explained that, several years earlier, Deucalion was the Alpha of his own pack of Betas, just as Kali and Ennis were. They had come to Beacon Hills for a summit with the renowned Alpha Talia Hale, representing the Hale Pack, and had apparently gathered early at Ennis' request to discuss their response against the Argent Hunters who had tortured and killed one of his Betas right in the Abandoned Distillery where they were meeting. Kali was reluctant to get involved due to the fact that the Beta wasn't a member of her pack, but Talia's daughter Laura Hale reminded them all that the Argents don't discern between packs, and that they were all considered the same to them.
Deucalion then argued that the Argents do discerned motive before asking Ennis what it was that the Beta did to earn the Argents' ire. One of Deucalion's Betas, Marco then revealed to the group that Ennis' Beta killed one of the Argents, though Ennis insisted that it was an accident. Talia agreed that it was within Ennis' rights to seek revenge for his fallen packmate, citing the fact that the Hunters were not the only ones who adhered to thousand-year-old rituals. Deucalion was totally against this, however, and argued that their history shouldn't give them an excuse for not evolving, reminding them that "it never ends with an eye for an eye" and that this skirmish could explode into a war that would make them no better than the Hunters they were fighting. Ennis, however, retorted that ripping his Beta's claws from his fingers wasn't evolving either and declared their debate to be useless before using his own claws to gouge a large spiral in the corrugated metal wall to warn others of his intent to get revenge.
Meanwhile, in the present day, Peter and Cora revealed to Stiles that Deucalion's Druid Emissary for both his original pack and the Alpha Pack was Marin Morrell, who happened to be the guidance counselor at the high school.
Back in the flashbacks, Deucalion and Talia had sought guidance from Talia's Emissary, Alan Deaton, who admired Deucalion's willingness to make peace with the Hunters but warned him that it might not be welcomed. Talia, agreeing with Deaton, pointed out that Gerard may not be the one to accept it; Deaton originally believed she thought this because the Argents operate under matriarchal leadership, but Talia corrected him by saying it was because he was a psychopath who bisects Werewolves with a broadsword.
Deucalion was disappointed in Deaton and Talia's lack of faith in people, believing that Gerard had to be concerned about the loss of life on his own side, but Deaton referred to the story of the Scorpion and the Frog-- just as the Frog underestimated the Scorpion's nature by thinking it wouldn't sting him, Deucalion must not underestimate Gerard's nature for treachery. Talia, agreeing with him, advised Deucalion to meet with Gerard on neutral ground and to not go to the meeting alone, but Deucalion wrly reminded her that, as an Alpha, he never walked alone. Deucalion then sent Deaton to arrange the meeting with Gerard as a neutral party.
However, despite Gerard's perspective on the story, he actually set a trap for Deucalion, his Betas, and even the Hunters who accompanied him. They met at the same Abandoned Distillery, which Gerard found fitting, considering distillation is a "separating of two substances by pushing them into their different volatile states." Deucalion admitted that "volatile" was exacting the state he was trying to avoid, which seemed to trigger Gerard's plan, because the older Hunter stated that he was about to be disappointed before setting off a huge cloud of Wolfsbane fog that affected everyone in the room, Werewolf and human alike. Gerard then gave himself some kind of antidote in his leg to prevent himself from being poisoned by the fog before grabbing a baseball bat with Werewolf claws embedded in it and using it to attack and kill both Deucalion's Betas and the two Hunters who accompanied him as well.
Deucalion, weakened by the fog, was appalled by Gerard's actions, and Gerard smirked and revealed that the Hunters also wanted peace as well, which was why they had to die with the rest of them. While Gerard finished off the others, Deucalion weakly crawled outside of the distillery, but Gerard was ultimately able to easily catch up with him. As Deucalion was flipped onto his back, he begged Gerard not to do this, insisting that he had a vision for peace. Seeing a perfect opportunity for a dramatic ending, Gerard smiled and stated that Deucalion's vision was a "little short-sighted" before plunging a flash-bang arrow into each of Deucalion's eyes, causing them to be burned from within as he screamed in agony.
A short time later, Deucalion, his Beta Marco, and Talia went to the Beacon Hills Animal Clinic, where Deaton gently removed the bandages from Deucalion's healing eyes, which were red and cloudy. The Emissary and veterinarian grimly informed Deucalion that, while his eyes may heal completely on a physical level, it was unlikely that he would regain his sight. Furious and embarrassed, Deucalion yelled at everyone to leave him alone, which everyone did aside from Marco, who made it a point of emphasizing that Deucalion was alone and that his weakened state gave him an opportunity to take over as Alpha.
He then attempted to attack his Alpha to steal his powers, but Deucalion, overwhelmed with anger, found to his surprise when he transformed that he was able to retain some sight (albeit color-blind and red-tinted) while in his Werewolf form, allowing him to viciously maul Marco to death, inadvertently absorbing his powers at the same time.
In the present day, Scott was shocked to learn that Deucalion could see as a wolf, and Gerard confirmed by reiterating "He's not always blind." Allison was certain they could use this against him and got up to leave, though Scott made sure to let Gerard know that he noticed his heart rate remained steady through the entire story, which told Scott that he was lying about how the events really occurred. He then went on to threaten to take away more than just Gerard's pain if he had mislead them or withheld information that could get people hurt.
In The Girl Who Knew Too Much, though Deucalion didn't physically appear, his presence and agenda still played an important role throughout the episode.
Ethan was at his locker when Aiden approached him and expressed his concerns about his brother's relationship with Danny Mahealani, specifically that it needed to end. Ethan argued that the young human was harmless and reminded Aiden that it was his girlfriend Lydia Martin they needed to worry about, which only supported Aiden's point that Ethan, having been assigned to get close to Danny, no longer needed to do so now that they knew Lydia was the key to get to Scott.
When Ethan insisted that Danny was harmless, Aiden realized that his brother actually did have feelings for the young man and demanded to know if Ethan would be able to go through with killing Danny if Deucalion asked him to do so. Ethan turned the question on Aiden and asked him if he would be able to kill him if Deucalion asked him to, causing a frustrated Aiden to back off, though he warned that if he didn't stop speaking to Danny, he would rip the flesh off his face and eat it, worrying Ethan about Danny's safety.
Later, when Lydia, on the suggestion of Scott and Stiles, met up with Aiden for their usual hook-up in hopes of gaining information on what was going on with the fight between the Alpha Pack and the Beacon Hills packs. The conversation inevitably devolved into the reminder that Ethan and Aiden were technically responsible for Vernon Boyd's death, but Aiden argued that it was Kali who made the call and he didn't have a choice. When Lydia pointed out that they were all Alphas, Aiden bitterly informed her that the pack wasn't as democratic as she would think, implying that Deucalion was at the top of the hierarchy and the twins were at the bottom.
Meanwhile, Scott and Stiles confronted Ethan in hopes that he would be more open to sharing information with them, since he seemed to be the most sympathetic one of the group. Scott assured him that he knew he didn't want to kill Boyd, and emphasized that he was sure that if something like that were to happen again, Ethan wouldn't do it. Ethan insisted that Scott didn't know what he and his brother owed Deucalion and the others, because they were Omegas when they first met him.
Ethan went on to explain that the two were Omegas running with a ruthless pack led by an even more savage Alpha when they met Deucalion, and that it was the Alpha of Alphas who taught them how to control their Merging power and allowed them to kill everyone in the pack, finishing their Alpha off last so they would become Alphas and could join the Alpha Pack. Scott asked if they killed their Emissary, too, and when Ethan confirmed that he did, he added that the only Emissary to survive was Marin Morrell, Deucalion's Emissary from his original pack who now provided guidance to the Alphas.
This led Scott to go see Morrell in the guidance counselor's office to try to get more information from her about what they could possibly do to defeat the threats they were facing-- the Alpha Pack and the Darach. Morrell snidely asked why Scott was wasting his time with her when he knew the clock was ticking when it came to the next person to be captured for the Darach's sacrifice. Scott, who had come to the conclusion that Morrell was the Darach due to the fact that they were looking for a Druid who had reason to hate the Alphas, insisted it was by her, leading Morrell to joke that he should leave the interrogation to Stilinski. When Scott once again asked if she was the one killing people, Morrell asked him if he was listened to her heartbeat before repeating that she was not killing people.
She then became honest with Scott, revealing that she was the only person who stood between Deucalion and Scott and the rest of his friends. Confused, Scott asked her why, and Morrell explained that Deucalion wanted a True Alpha in his pack and that he thought it was Scott, and that the Darach's human sacrifices wouldn't distract him from his goal. Scott insisted that he wasn't an Alpha, but Morrell just gave him a knowing look and stated that he was well on his way to being one, and they both knew it. Scott, getting frustrated, demanded to know what Deucalion was waiting for and what he wanted, and Morrell's tone of voice became serious when she replied, "He wants to make a killer out of you. That's what he does."
Scott assumed that if he killed someone, then he wouldn't be a True Alpha anymore, a theory that Morrell confirmed before stating that this was exactly her point. She went on to ask him if he wanted a psychologist's perspective and gave it to him before he could respond-- "He's an obsessive who both desires you and is threatened by you. If the obsessive can't have the object of his desire, he'll choose to destroy it instead."
This brought Morrell to Deucalion's grand scheme: either Scott willingly became part of his pack as a True Alpha, or Deucalion would force him to kill and destroy his potential to become a True Alpha. Scott insisted that neither of these options were going to happen, but Morrell advised him not to be so confident, as he was playing Deucalion's game, and while Scott and his friends were scrambling to deal with events as they occurred, Deucalion was already thinking ten moves ahead and had checkmate in sight.
However, the Beacon Hills packs' attention was diverted away from the Alphas and toward the Darach when they realized that she was in the middle of killing her three "Philosopher" sacrifices, forcing them to reconvene at the high school, where the Darach was revealed to be Jennifer Blake when she took Lydia captive and planned to kill her for knowing too much. Lydia pleaded with Jennifer to stop, but Jennifer simply stated that she wished she could, but that Lydia didn't know Deucalion like she did.
Just as Jennifer was about to slit Lydia's throat, Lydia let out a deafening scream that caused the Darach to realize that Lydia was a Banshee, also known as the Wailing Woman, a supernatural Harbinger of Death. Though Scott, Stiles, and Stilinski managed to distract her enough to rescue Lydia, she captured Stilinski to use as her final trio of "Guardian" sacrifices, believing that once she was finished with the ritual, she would have the power needed to defeat Deucalion.
In The Overlooked, Beacon Hills Memorial Hospital was in the process of being evacuated due to a raging storm outside, and Jennifer Blake, who had been exposed as the Darach, was dragged to the hospital by Derek, Scott, and Stiles, who were intent on forcing her to heal Cora from what was revealed to be mistletoe poisoning before telling them where she was holding Stilinski hostage.
The three met up with Peter, who was doting on Cora when the Alpha twins, Ethan and Aiden, showed up, presumably on Deucalion's orders, looking for Jennifer. In the chaos caused by Derek and Scott jumping in to fight the twins, and Peter and Stiles checking on the unconscious Cora, Jennifer was able to escape.
She made it down the elevator to the ground floor, where she ran into Deucalion and Kali. Deucalion threw his dagger-tipped cane at her like a javelin, and Jennifer just barely managed to dodge it, causing it to instead embed itself into the wall next to the elevator. She then backed into the elevator once again, and when Kali lunged for Jennifer on Deucalion's orders, Jennifer slammed her hands against the door with her superhuman strength gained from the Five-Fold Knot Sacrifice Ritual, creating a concussive force that threw Kali backwards down the hall, where she landed at Deucalion's feet.
Melissa McCall stumbled upon the cane still stuck in the wall and pulled it out, looking at it with curiosity and concern. Suddenly, Deucalion and Kali appeared behind her, and the former thanked Melissa for returning the cane to him as he took it back and returned the cap that covered the small blade at the tip. Melissa, having heard about Deucalion, asked him if he was the bad guy, leading Deucalion to smirk widely and retort, "You have no idea." As the lightning flashed, Deucalion and Kali's glowing red eyes were visible in the opposing flash of darkness that followed.
Scott, Stiles, Derek, Peter, and the unconscious Cora had run from the twins and stopped in a nearby operating room to regroup, where they began arguing about what they needed to do next. Their tense debate was interrupted when Jennifer appeared and reiterated that she was the only one who could cure Cora and tell them where Stilinski was located. When Stiles insisted she prove it by healing Cora, Jennifer retorted that she would only do so when she was out of the hospital and safe from the Alphas, as she knew she needed leverage to get their protection from Deucalion and the rest of the Alpha Pack.
Derek and Peter were about to agree that torturing Jennifer was the way to go when Melissa's voice was heard over the PA system, anxiously saying, "Um, can I have your attention? Mr. Deucalion... excuse me, just Deucalion... requests you bring the woman calling herself Jennifer Blake to the ER reception. Do this, and everyone else can leave. You have ten minutes."
Everyone in the room looked at her furiously, and Jennifer, realizing that this was conflicting with her goal of getting out of the hospital safely, immediately argued that Deucalion wasn't going to hurt her; when Derek and the others are loathe to believe her, Jennifer turned to Scott and ordered him to tell the others that it was the truth, forcing Scott to confirm that he was a True Alpha and that Deucalion was seeking him out for his pack along with Derek.
This distracted the group for a few minutes until Scott reminded them that they still needed to get Jennifer safely out of there if they wanted to save Cora and Stilinski. Stiles was also concerned about Melissa, but Scott believed that they can split up, with one group distracting the Alphas and trying to get Melissa back while the other used the last ambulance as part of the evacuation to get Jennifer out of the hospital without Deucalion or the others catching them. It ended up being Scott and Peter fighting off the twins while Jennifer escaped with Derek to the basement loading area along with Cora and Stiles.
On the roof, Deucalion supervised as Melissa, under his orders, shut off the power to the entire building, causing the generator to kick on only to provide light inside. He thanked her for her cooperation and then allowed her to leave, referring to her as his "gesture of goodwill" to show Scott that he was a man who could keep his promises. Melissa was confused by this turn of events, but Deucalion simply urged her to go find her son before advising her to be careful out in the storm.
Meanwhile, Stiles and the unconscious Cora holed up in an ambulance in the basement loading area while Derek and Jennifer, forced to flee due to Kali killing the ambulance driver, ended up in the elevator, which got stuck between floors when the power was shut off. Deucalion ended up meeting back up with Kali in the morgue, while Scott, separated from the others after sending Peter to watch Stiles and Cora, reunited with Melissa and were joined by the late arrivals Argent, Allison, and Isaac in one of the operating rooms to regroup once again.
Down in the morgue, Kali criticized Deucalion for letting Melissa go, believing they should have kept her as leverage, but when Kali remarked that Deucalion had a soft spot for Scott, Deucalion retorted that he had an investment he was trying to mature by showing him that he was a reasonable man.
Deucalion then turned the topic to Jennifer and the fact that Kali had, just minutes earlier, confirmed that the Darach was actually her former Druid Emissary who was then known as Julia Baccari. During their discussion, it was revealed that Deucalion had made Kali kill Julia/Jennifer as part of her initiation into the Alpha Pack, something Kali had never understood, as she believed her former Emissary was harmless. When Deucalion brought up the fact that she was hardly harmless now, Kali admitted that she did think that Julia was dead after attacking her, but she did feel a moment of uncertainty and ultimately decided to allow Jennifer to "die peacefully" rather than give her the killing blow. Deucalion sarcastically stated, "My heart bleeds for you, Kali. Apparently, hers could have bled a little more."
While the main group finalized their plan, which involved Allison switching clothes with Jennifer and pretending to be her to lure the Alphas outside where she and Argent would start firing upon them with their respective weapons, while Jennifer and Derek (along with all the others) fled through the back of the building while they were occupied. However, Deucalion seemed to have heard their plotting and had at least some idea of what it was they were about to do.
Nevertheless, the plan ultimately worked out almost completely as they planned, with Kali and the twins following Allison outside so that she and Argent could fire at them with arrows and bullets. Meanwhile, Isaac would take the Argents car to the pack and pick up Stiles, Cora, and Peter before swinging around to get the Argents before ultimately meeting up with Derek and Jennifer at a meeting place nearby.
However, the plan went somewhat awry starting with Jennifer double-crossing Derek, knocking him out and escaping through the elevator hatch on her own. Then, Scott and Stiles realized that the entire plan was a ruse for Jennifer to capture Melissa as her second "guardian" sacrifice and ran to the roof, only to find Jennifer gone and Deucalion standing there alone.
Deucalion used Scott's devastation at losing his mother to convince Scott to join him, insisting that he would be able to help Scott get both Melissa and Stilinski back, knowing that by doing so, he'd be taking the first steps to getting Scott to trust him and then ultimately join the pack entirely. Stiles begged Scott not to go with him, insisting that they could figure it out and come up with a plan B as they always have, but Scott, believing they were out of options, simply assured Stiles that he would get Stilinski back safely before leaving with Deucalion.
In Alpha Pact, Deucalion had managed to convince Scott to join his side, just like he had planned from the beginning. After the battle between the packs in the hospital, Deucalion unleashed a howl to warn his fellow Alphas that it was time for them to retreat.
The next evening, Deucalion was joined by Kali, Scott and the twins in tracking down their Emissary, Marin Morrell, who seemed to know more about Jennifer's plans in regards to taking down the Alpha Pack than she was letting on. However, Marin anticipated such thing from them and managed to evade them for quite a while in the woods.
While chasing after Morrell, Deucalion and Scott spotted a firefly that was unusual in the region of California. Scott brought up the events that happened when the Alpha Pack and Jennifer made their first appearances-- the deer that crashed into Lydia's car, the cats' agitated behavior in the animal clinic and the ravens that committed suicide by flying into the windows of the high school. Deucalion hypothesized that since animals could predict natural disasters, they could also sense the supernatural ones. When Scott asked Deucalion if Jennifer scared him, Deucalion denied such thing and insisted that he was "concerned" with the fact that Jennifer was willing to kill innocent people, like Scott's mother Melissa and Sheriff Stilinski, with the goal of taking him and his packmates down. Scott looked nervous and had one more question for the Alpha Pack leader, "Are you willing to kill innocent people?", earning the response, "I will kill any living thing that gets in my way."
After Marin ran into a dead end, she realized that the Alphas were getting closer and reached out to some Mountain Ash in her pocket before using to create a perfect circle around her. Once the twins spotted her, they lunged at her, only to be repelled by the mystical forces of the Mountain Ash circle. Kali, Duke, and Scott joined the scene and the blind Alpha immediately demanded answers from the Emissary of his original pack. Morrell insisted that the Alphas were always suspicious of Druids like herself and Jennifer for what they were capable of doing, leading Kali to remind her that she gave them good reasons to come after her, like when she hired Braeden to save Isaac from their clutches several weeks ago. Marin continued to argue that her intentions were for the greater good and to keep up with her mission as a Druid-- maintain the balance of Nature.
Once Marin finally came clean with them and revealed that she had no idea where Jennifer could be at the moment or what she could be plotting against them, she looked at Scott and asked him to return to his friends, arguing that the Alpha Pack did not share his mission of protecting the innocent. Deucalion interrupted her and assured her that Scott could decide what was the best for himself, to which Marin shot back with the fact that Duke had not fully informed Scott of the numerous corpses that the Alpha Pack leader had piled up in his "narcissistic and psychotic" goal to achieve the "perfect pack." She attempted to tell the other Alphas that Deuc did not care for any of them genuinely and was perfectly comfortable with killing them if necessary for his plans, just like he had done to Ennis, explaining that Deaton had succeeded in saving Ennis before Deucalion came to the clinic to kill his fellow Alpha. He used Ennis' death as the perfect way to further motivate Kali as well as the twins in the pack's task to recruit Derek, whose membership in the Alpha Pack would allow Scott to join them as well.
The Alphas and Scott were shocked by such revelation but Deucalion managed to remain calm and shrugged off Marin's story as a lie told by a woman who was begging for her life. Marin remained undeterred and encouraged the Alphas to learn the truth for themselves, which became the last straw for Deucalion, who removed the bottom cap from his cane and single-handedly threw it at Marin. The cane's sharp blade lodged itself in Marin's shoulder, causing her to fall to the ground and inadvertently break her Mountain Ash protection. The Alphas growled and were prepared to finish her off, though Scott managed to rush to Marin's side and ordered his new packmates to back off; surprisingly and miraculously, they did listen to Scott.
Scott removed the cane from Marin and reassured her that he would not let the Alphas take her life but asked if she possessed any information that could be useful against Jennifer. Seeing Scott's desperation to save the parents, Morrell instructed him to find the Nemeton because it would be there where Jennifer was holding the guardians captive.
In Lunar Ellipse, afte barely surviving the surrogate sacrifice ritual to find the Nemeton and the parents, Scott informed his packmates that he had made a deal with Deucalion to find the parents, adding his belief that the Alphas were going to be necessary allies in order to take down Jennifer once and for all. Both Stiles and Isaac were in agreement that this was a terrible idea, and the latter incredulously asked, "So, we're gonna trust him? The guy that calls himself, "Death. Destroyer of Worlds?" We're gonna trust that guy?" Deaton offered a piece of advise-- they could use the corrupted Alpha as bait even though he was an enemy of theirs as well.
Their debate was unexpectedly interrupted by the arrival of Ethan, who, unlike Aiden and Kali, had believed in Deucalion's role in Ennis' death. He immediately went to the point of his visit-- he needed Lydia's help in dissuading Aiden from helping Kali in killing Derek.
Since Derek was downgraded back to a Beta after he was forced to sacrifice his Alpha spark to heal Cora, Ethan and Lydia agreed to remain behind in the loft and give the Hales enough time to drive away from Beacon Hills. Once Kali and Aiden arrived to the loft, Jennifer made her appearance and a huge fight broke out between the Darach and the Alphas.
Despite the Alphas' best efforts, Jennifer proved to have become superior to them and she managed to take down the twins in their merged form by putting them in a backward headlock and breaking their neck over her shoulder. Right after, Jennifer gave Kali a chance to apologize for trying to kill her during her initiation into the Alpha Pack, but the toe-clawed Alpha, despite showing remorse for what she did to Jennifer, screamed that she should have ripped Jennifer's head off, infurating Jennifer to the point that she telekinetically launched the shards of glass from the broken skylight of the loft into Kali's entire body. These wounds were ultimately fatal to the Alpha and she collapsed on the floor of the loft, dead.
Jennifer scared Lydia into screaming to lure Derek and Cora back to the loft. Jennifer showed the dead Alphas as enough motive for Derek to team up with her as her single living guardian against Deucalion, only for him to viciously once again reject her offer. Once Jennifer made it clear that he would be helping Scott and swore to spare the lives of the parents as long as Derek remained by her side, Derek begrudingly agreed to her terms.
Meanwhile, Deucalion met with Scott, Isaac and Allison at the Look-Out point of the woods, joking that he and Scott were "cutting it a little close." Scott apologized for taking so long in meeting with him and asked where the other Alphas were, to which Deucalion responded, "Occupying themselves with other pursuits." Scott was surprised to see that he and Deucalion would be the only ones against Jennifer but Deucalion assured him that they would make a great team. Before leaving, Scott instructed Allison and Isaac to find Stiles and get to the root cellar as fast as possible while he and Deucalion took care of Jennifer long enough for the parents to be rescued. When Isaac frowned in concern and asked his close friend and foster brother in how he would do that, Scott cryptically stated that he had a plan.
When the two arrived at the Abandoned Distillery, the very same place where Deucalion lost his eyesight at the hands of Gerard Argent, Deuc wondered what Scott was planning and he explained that during his first junior year class, Jennifer sent him and his classmates an excerpt of the novel Heart of Darkness from Joseph Conrad and now he had a message to send her. In the woods, Derek and Jennifer were watching the countdown for the lunar eclipse until she received a video from Scott, who showed them the spiral that Ennis had carved into the wall with his claws while transmitting the following message, "You see this symbol? It's a symbol of revenge. You talk about balance, about saving people... We know what you really want. And now, you know how to find us." Jennifer's enraged expression made it clear that she was more than ready to take Deucalion down once and for all.
Deuc and Scott patiently awaited for Jennifer in the middle of the distillery, though Scott became confused when he noticed a second figure walking alongside Jennifer toward them through the blowing window. Once Derek and Jennifer emerged, Scott became perplexed over the news that Derek was willing to team up with the woman that poisoned his own sister and Derek confirmed that although it would be hard to believe in what he was doing, he was actually trying to help him, which certainly amused Deucalion, who remarked that a showdown between brothers was quite American. Deucalion folded his cane, removed his coat and put them aside while asking Jennifer if she was ready (specifically, if she had gathered her herbs, prayed to her ancient gods and oak trees and/or slit a baby's throat), and if they should show everyone if it was really worthy sacrificing twelve innocent people with the sole purpose of facing him while transforming into his "Demon-Wolf" form, with red eyes that cover both his irisis and pupils, dark blue-black skin and pronounced muscle definition.
The battle began, with Derek wolfing-out and lunging for the Alpha Pack leader. Unfortunately for him, he did not stand a chance against the more powerful Alpha now that he was returned to Beta status, having both of his arms pinned down by Deucalion. Seeing Deucalion was distracted battling Derek, Jennifer moved in and attempted to strike him with her telekinesis, just like she did earlier with the other Alphas; much to her horror, her power did not affect Deucalion at all and the demonic Alpha lifted both Derek and Jennifer by the throat for several seconds before dropping them. Once Deuc had tossed Derek aside, he striked Jennifer hard and bested her rather easily. He wrapped his hand around Jennifer's hairs and brought her before Scott, who simply watched the whole confrontation, demanding the young Beta to kill her.
When Scott silently refused, Deuc used his Alpha Roar to force Scott to shift against his will before repeating his order. He attempted to tell him that Jennifer was using her connection to the Telluric Currents to create the storm above them as well as to bury the parents alive-- if Scott killed her, the connection would be severed and he would save his loved ones. However, Jennifer pleaded with Scott, insisting that her death would not change anything and would simply condemn his loved ones to death, just like Deuc wanted since, accoridng to her, it is part of his nature. Deucalion kept trying to sway Scott, insisting that he had to become an Alpha and killer in order to save everyone. Scott confidently stated that the parents were not dead yet and when Deucalion asked if it would be his friends to save them, Scott proudly declared, "My pack."
The unpleased Deucalion rushed toward Scott with his unbelievable speed and grabbed his right hand while forcing to walk straight toward Jennifer. However, Scott stopped him and brought up what he had forgotten to tell Deuc, something that he had learned with Gerard-- Deucalion was not always blind. With his free left hand, Scott reached out to some flash-bang arrowheads and dropped them to the ground, blinding the three Werewolves for a few moments. The lunar eclipse just started and three were returned to their human forms before realizing that Jennifer went missing.
A few moments later, Jennifer returned in her Darach form and wasted no time in unleashing her immense power upon the powerless wolves, sending Scott flying toward some palettes before setting her sights on Deucalion. She smacked his head against the cement floor several times and would have killed him had Derek not stopped her. Derek reminded Jennifer that Deucalion had never come to see the price Jennifer's face had paid following Kali's attack on her, encouraging Jennifer into healing Deucalion's eyes. The Alpha screamed in pain for a brief moment and whimpered until his eyesight was restored for the first time in nearly a decade.
Deucalion looked noticeably shocked and surprised that he was capable of seeing with his human vision once more, allowing him to see Jennifer's dehumanized and scarred face that she had acquired from his efforts to form the Alpha Pack. Surprisingly, Jennifer hesitated when she was about to give the killing blow to Deucalion and was shown to have been weakened to the point that she could not kill him, just like Derek had intended. Still believing Derek to be on her side, the weakened Jennifer asked him to end Deucalion's life for her, but, much to her shock, Derek denied her request, quoting his mother, Talia Hale, "I'm a predator. I don't have to be a killer." Derek furiously grabbed Jennifer by the throat and ordered her to free her hostages, but the enraged Jennifer quickly got the upperhand and slammed Derek against a crate before slapping him in the face many times out of anger for his betrayal.
When the eclipse had ended, Jennifer vowed to kill the parents in order to acquire the power necessary to end Deucalion and everyone else. The former blind Alpha began witnessing Scott's efforts to push through Jennifer's Mountain Ash circle and his indomitable willpower allowed him to ultimately succeed in breaking through Mountain Ash, ascending to True Alpha status at last, much to the shock and surprise of both Derek and Deucalion. Scott declared that he was an Alpha now and gave Jennifer an ultimatum-- either she voluntarily stopped the storm or he would finish her off himself, despite the potential danger of ruining his newly-acquired Alpha rank. Having realized how unique Scott truly is, Deucalion insisted that nothing would change the color of his eyes and clawed Jennifer's throat out himself, saving Scott the trouble.
After Derek and Scott got a call from Stiles and were reassured that they were all alive, they spoke to Deucalion, with Derek bringing up how his mother spoke of Deucalion as a "man of vision" and expressing his hope that he could be that man again. However, they did not leave before Scott threatened Deuc that they and their friends and allies would come after him if he proved to have not changed at all, regardless of his regained eyesight.