In Muted, Parrish was staking out the Walcott House to make sure that the killer of three of the four members of the Walcott Family didn't return to the scene when he suddenly saw someone inside the house. When he burst inside and identified himself as a Sheriff's deputy, he was shocked to see Lydia (who looked horrified to find that she had just snapped out of a Banshee fugue state) come out from the adjacent hallway.
After the shock had worn off, Lydia remarked that she would try to explain why she had been drawn to the house, but she had yet to receive a satisfactory explanation herself. When Parrish pointed out that all she had was an unusual habit of showing up at the sites where brutal murders took place, Lydia raised an eyebrow at him and asked if that meant she had a reputation. Parrish assured her it was simply an unusual one before suggesting that she might be psychic, causing Lydia to flirtatiously ask him if he really believed in that. Parrish, who had already been witness to supernatural events that couldn't be explained, stated that he didn't want to believe in anything but tried to keep an open mind anyway. This led Lydia to start to warm up to him just before she noticed what looked like screaming faces in the grain of the wood on the wall behind Parrish.
Lydia wandered toward it, looking at the wall as if she was receiving another premonition from the Banshee figures in the wood grain until she finally got the idea to press on it. This revealed that there was a hidden door in the wall that caused a small amount of cold fog to seep out, and Parrish instantly pulled out his gun before walking through the door with Lydia following closely behind.
They walked through the chilly secret corridor before coming to a doorway covered by strips of clear plastic, and once inside, they found large bags hanging from hooks. Parrish suggested that it was a game locker, since hunting large animals is legal in some parts of California, but it was obvious that Lydia knew the contents of the bags didn't hold the kind of animals Parrish was thinking about. This led her to be disgusted, but not surprised, when Parrish opened the nearest bag to find a dead woman hanging from the hook inside, revealing that the Walcott family had been cannibals, specifically a cannibalistic species of shapeshifter called Wendigos.
In I.E.D., Parrish found Meredith Walker, who had escaped from Eichen House after receiving a Banshee premonition that Lydia and Malia Tate needed her help, while she was walking toward downtown Beacon Hills. When Parrish brought her to the Sheriff's station, he was surprised when Meredith wasted no time before telling Sheriff Stilinski that she needed to talk to Lydia.
Later that evening, Parrish approached Stilinski, where he observed that the Sheriff had, in fact, contacted Lydia and Malia with instructions to come to the station. Stilinski frowned when Parrish asked if he called Lydia "because Meredith asked for her, or because of the other thing," and when he asked what Parrish meant by "other thing," Parrish looked around to make sure he wasn't being overheard before replying "The psychic thing." Sheriff Stilinski was surprised to hear that Parrish believed Lydia was psychic, but when Parrish asked him if he thought Lydia was psychic as well, Stilinski tried to backtrack by claiming that Lydia was simply "intuitive." This led Parrish to point out that psychics used to be called "intuitionists," and Stilinski, frustrated by this entire situation, simply invited Parrish into his office to observe Lydia and Malia talking to Meredith.
Once inside the office, Parrish watched as Lydia surreptitiously handed Meredith her phone, as she knew that Meredith used phones to make sense of her auditory Banshee premonitions; however, Parrish was confused when Meredith simply whispered, "It's not ringing." Lydia continued to encourage Meredith to help them figure out the second cipher key to the Deadpool hit-list code, but she became frustrated when Meredith pointed out that she had come because she heard Lydia calling for her, once again confusing Parrish. However, he sensed the frustration of both Banshees and stepped in to try to mediate, kneeling in front of Meredith and asking her if he could ask her a question, which Meredith nervously allowed. Lydia seemed genuinely surprised and impressed by Parrish's patience as he asked Meredith if there was someone she reached out to or called when she needed help finding something. When Meredith admitted that she contacted different people depending on what kind of assistance she needed, Parrish asked her if that meant that maybe there was a number that they could call for help as well. Meredith nodded and gave Parrish, Lydia, and Malia the numbers 2-4-3-6.
However, since this wasn't a full phone number, Lydia once again lost her patience, reminding her that a lot of people were going to die if she didn't help, but Meredith continued to insist that the number she gave was it, eventually shutting down completely and forcing Parrish to intervene to calm Meredith down while also sending Lydia and Malia out of the office to cool off. Sometime later, when Malia figured out that the number Meredith gave them corresponded with telephone keys and spelled out "Aiden," Lydia used the code to unlock the second list in the Deadpool. After Malia left, Lydia was scrolling through the list when Parrish came in, startling her so badly that she slammed the laptop shut at the sound of the door opening. Parrish apologized for scaring her and asked her if she needed a ride home, but Lydia smiled nervously and assured him that she was fine. When Parrish left, she opened her laptop and anxiously bit her lip as she reread the names and bounties on the list. Included on the list was "Jordan Parrish," who had a bounty of $5 million.
In Orphaned, Lydia and Stiles, knowing that unlocking the last third of the Deadpool hit-list was necessary in order for them to stop it, returned to the Sheriff's station. Upon seeing them, Parrish informed the two that Sheriff Stilinski was out, but that they were welcome to wait until he returned, but Stiles and Lydia instead informed the young deputy that they were there to talk to him. They gave him a folded print-out of the second portion of the Deadpool that they had unlocked in the previous episode, explaining that it was indeed a hit-list before asking him if he recognized any of the names. Parrish remarked that Sheriff Stilinski did have him run some of those names through the system earlier, though none of them had records. Stiles gave Lydia a look and told her to show Parrish "the other thing," which led Lydia to gingerly flip the folded list over to show Parrish that his name was on the hit-list as well.
Parrish immediately declared this newest revelation to be "kind of terrifying" before asking them what the number meant. Lydia hesitated before stating that it was what he was worth, and Parrish was momentarily offended that he was only worth $5 before they corrected him by saying he was actually worth $5 million. After Parrish lamented the fact that he only made $40,000 a year and suggested killing himself to get his bounty, he asked them why he was on the list in the first place, but Lydia and Stiles decided to introduce him to the supernatural world another day and instead focus on cracking the third and final list. Parrish seemed eager to help them figure out the key until Lydia nervously pointed out that they needed Meredith Walker's help again. Parrish exasperatedly reminded her that she had nearly given Meredith a nervous breakdown the last time she talked to her, but when Lydia emphasized the "almost" in his statement, Parrish sighed and agreed to escort the two to Eichen House to interview Meredith again.
When the three of them got to Eichen, they were in the process of being let into Meredith's room in the closed unit by an unnamed orderly when the head orderly, Brunski, approached them and immediately stopped them. Parrish insisted that they needed to talk to Meredith as part of an investigation into a murder, and though Brunski conceded that Parrish could go in if he wanted, Lydia and especially Stiles had to stay behind. Parrish argued that they were crucial witnesses in an ongoing investigation and pointed out that he wouldn't have brought them if he didn't have to, but Brunski wasn't convinced and stated that if they wanted it, he would have to come back for a warrant. When Parrish saw Brunski taunting Stiles for his previous stint in the mental health center and his outstanding bills, Parrish brought up the fact that a buddy of his at Canaan police department told him he helped Brunski get home after blowing a 0.1 on a breathalyzer test, impressing Lydia and Stiles before Brunski caved and allowed them entry into Meredith's room.
However, upon sitting down to talk to Meredith, Lydia immediately became frustrated by Meredith's lack of desire to help them, which made Parrish nervous enough to tell them to go easy on her. Lydia pointed out that Meredith had helped them out before, and she and Stiles both were flabbergasted when Meredith implied that things had changed since then. After some coaxing, Meredith finally admitted that "he" didn't want her to help them with the Deadpool anymore, leading Parrish, Lydia, and Stiles to realize that she had been in contact with the Benefactor. She starts to have a panic attack from all of the pushing Lydia is doing, which only makes Lydia more desperate for answers. It wasn't until Meredith screamed "I don't know!" in her Banshee voice that they finally stopped, because the force of the scream caused Lydia's ears to start to bleed, leading Parrish to insist that they leave.
That night, after Lydia got a Banshee premonition that led to the realization that the final cipher key was "Derek," she and Stiles used the key to unlock the last portion of the Deadpool list, which included Meredith (whose bounty was $1 million). Lydia immediately insisted that they needed to call Parrish to inform him of this newest development, but when she did, Parrish was forced to apologize to her before breaking the bad news that Meredith had been found dead at Eichen House by Brunski after the girl hung herself with her sheet.
In Perishable, Lydia was at the Beacon County Sheriff's Station with Stiles and Sheriff Stilinski, discussing the computer code that Lydia's grandmother, Lorraine Martin, had left for her, when Parrish, who had been the victim of a Deadpool assassination attempt at the hands of Deputy Haigh, arrived totally naked and covered in soot. He immediately tackled Haigh in a furious trance (possibly due to the Hellhound spirit inside of him) and began to wrestle Haigh's gun out of his hands. Just as the Sheriff, Stiles, and Lydia ran out into the bullpen to see what the commotion was about, the gun went off and accidentally caused the Sheriff to get hit with the shot, though the battle didn't end until Parrish managed to punch Haigh into unconsciousness.
Afterward, Lydia brought Parrish to Derek's loft so that Derek and Scott could try to figure out what Parrish's immunity to fire meant for his supernatural identity. When Derek was shocked to learn that Parrish had survived being doused in gasoline and set on fire, Lydia brought up the fact that Parrish's hair and nails, the parts of the human body that are essentially dead, should be long gone due to the flames. Lydia, Scott, and Derek then informed Parrish about the fact that the reason why he was on the Deadpool was because he is a supernatural being, during which time Lydia admitted that they had lost track of all the various assassins who had flooded Beacon Hills.
The topic then turned to the code itself, which led Lydia to tell Parrish, Derek and Scott about the code left for her by Lorraine and the connection between Lorraine, who Lydia had just learned was a Banshee as well, and fellow Banshee Meredith Walker. While Lydia told the story, Parrish realized that it was the death of Lorraine's wife Maddy that caused Lorraine to become obsessed with the occult in search of an explanation for her powers, as she had a premonition of Maddy's death but did not take it seriously due to not being aware of her own supernatural nature.
The next day, Stiles and Lydia, who had just cracked Lorraine's code, brought the newly unlocked list of names to Parrish at the Sheriff's station in hopes that he could help them find a connection between them, as Lorraine's own name was on it. After looking into the names on the list, Parrish informed them that the only thing they had in common was that they were all dead after having committed suicide at Eichen House. This caused Stiles and Lydia to go to Eichen in hopes of bribing the head orderly, Brunski, into letting them look at the patient files of the dozen or so people on the list and possibly gain additional information about the victims.
Unfortunately for them, this visit caused the two to realize that Brunski was the person who created the Deadpool tapes, a realization that led them to incorrectly assume that he was the Benefactor. Realizing he had been caught, Brunski was about to kill Stiles and Lydia by giving them an overdose of sedatives, when suddenly, Parrish, who had discovered that Brunski had signed off on all the so-called "suicides" at Eichen and that he had actually murdered them as an "Angel of Death," arrived and saved them just in time by shooting the main in the chest. Afterward, Stiles, Lydia, and Parrish watched in horror as Meredith Walker appeared and confessed to being the real Benefactor, adding that while Brunski wasn't on her list, he was a bad person, implying she believed he deserved his fate.
In Monstrous, Lydia had ignored both Parrish and Stilinski's orders to go home and get some rest in favor of staying at the Beacon County Sheriff's Station, where the deputies were holding Meredith Walker. Lydia and Stilinski were in the middle of debating how to proceed when Parrish returned and admonished her for not having left the station yet. Lydia insisted she would not leave until Meredith finally started talking, and though Stilinski tried to argue that they would let her know as soon as she said anything, Lydia demanded to talk to her herself, reminding them both that she had gotten through to Meredith before, leaving Parrish and Stilinski with no choice but to allow Lydia to do as she asked.
The two stood by as Lydia went into Stilinski's office to speak with Meredith, explaining that she had begun to get an idea of how everything happened. She went on to guess that Meredith used Brunski, as she knew he had killed people and that he would do it again. She believed Meredith got Brunski to steal the computer code from Lydia's grandmother Lorraine, put it online, steal the money from the Beacon Hills Hale Vault, turn the bearer bonds into cash, and make the payments to the various assassins as they took out each person on the Deadpool list. She went on to ask Meredith if it was Brunski's idea to fake her death after he got nervous when she helped them with the second cipher key. Meredith assured Lydia that she only wanted to help, and Lydia agreed with her before reminding her that she wouldn't be there if she didn't want to talk. Meredith confirmed this suspicion before stating that she would only speak with one person-- Peter Hale.
Peter ultimately agreed to sit down and talk to Meredith with some convincing from Lydia and Stilinski in the Sheriff's station's interrogation room. Meredith was shocked to see that the burns on Peter's face had healed, and when she reached out to touch his face, Peter roughly grabbed her by the wrist before she could do so, causing Parrish to rush in and hold Peter at gunpoint before demanding that he let her go. When Meredith once again stated that she couldn't believe the burns were gone, Lydia realized that Meredith and Peter had met each other before-- when Peter was in a coma following the Hale House Fire.
Before anyone could process this further, Peter performed the Werewolf Memory Manipulation ritual on Meredith by inserting his claws into the back of her neck, and when Parrish attempted to separate them, Lydia rushed into the room and stopped him, informing him that breaking the connection early could kill both of them.
When Meredith quietly started whispering, Lydia realized her Banshee powers of Clairaudience allowed her to hear what Meredith and Peter were seeing in Meredith's memories and narrated the scene to Parrish and Stilinski-- Meredith, after being injured while being tested by Lorraine at the lake house, was put in the same room as Peter while he was healing from his burns in a coma. Somehow, Meredith's telepathic abilities allowed her to hear every thought Peter had, and since he was essentially trapped in his mind while he was in a coma, he had begun to spiral into insanity. His anger toward his sister Talia for being blind to the threat of the Argent Hunters had morphed into a desire to destroy the supernatural community as it was and remake it in his image, which ultimately gave him the idea to create the Deadpool.
He went on to explain this idea to Meredith, who, suffering from her own mental illness as a result of her traumatic injury, took it upon herself to set it into motion once she saw how devastating the supernatural could be when Lydia screamed for Allison's death at the hands of the Oni. When Peter snapped out of the memory, Lydia and Parrish realized that it was Peter's idea to start the Deadpool all along, leading to an argument brewing between Peter and the others. When Stilinski aimed his gun at Peter's head, Lydia insisted that they had to let Peter go to ensure that Meredith's true plan-- that Lydia, Parrish, and Meredith get killed in this fight and add three more supernatural deaths to the Deadpool-- would not come to fruition, leaving Stilinski with no choice but to relent, though he did threaten to take Peter out if he did something like this again.
In A Promise to the Dead, Parrish found Argent dying in the sewers after Peter had stabbed Argent with a piece of rebar and bend it to keep him from leaving and telling the McCall Pack that Peter and Kate Argent were working together to kill Scott. When Argent asked Parrish how he found him, Parrish revealed that he had not stopped tracking Peter since he nearly killed Meredith in the previous episode. Parrish was unable to bend the rebar on his own without assistance, forcing him to convince Argent to help him by using whatever adrenaline he still had in his body after fighting the effects of his injury to stay alive.
Exhausted and in shock, Argent weakly argued that he had nothing else to fight for, so Parrish, having been told about what happened to Argent's daughter Allison from Allison's best friend Lydia, used Allison's memory to encourage Argent to keep fighting. This argument ultimately worked, and the two men used their combined strength to free Argent, not realizing that by doing so, Parrish had activated his still-undiscovered Hellhound powers (namely his glowing fiery eyes and superhuman strength.
In Smoke and Mirrors, though Parrish and Lydia did not have any interaction during the main battle at La Iglesia (as Lydia had been purposely trapped at the high school by Peter Hale to prevent her from using her powers to warn the McCall Pack that he and Kate Argent were the threat, while Parrish accompanied Argent to Mexico to fight on the side of the Calavera Hunters.
However, once the dust had settled, Lydia brought a newly-created hardcopy book version of the Argent Bestiary to the Sheriff's station, explaining that the mystery of what kind of supernatural creature Parrish was could be in the book, and that she really wanted to help him figure out what he was.