In Parasomnia, Liam and Mason walked into Ken Yukimura's history class at the high school, where Liam found that the only available seat was next to his long-standing rival, Hayden Romero, much to Mason's amusement. When Hayden scowled at him, Liam stood awkwardly in the aisle until Mr. Yukimura instructed him to sit down, not noticing that Hayden had stuck her recently-chewed bubblegum on the seat until after he was seated. When he realized that he had sat on the gum, which was now all over his jeans, he looked at Hayden in exasperation to find her smirking, visibly satisfied by her small revenge.
After class, Liam ran into Hayden again when he was going to his locker to put his stained jeans inside, and she joked about the fact that he was forced to wear his gym shorts. Liam changed the subject to their yet-unrevealed past history and remarked that he was wondering whether she was still angry about what happened between them in the sixth grade before stating that the gum situation had answered his question. Hayden then fake-smiled at Liam and retorted, "I'm not angry, Liam... I'm vengeful" before she slammed her locker door shut and walked away. Afterward, Liam was seen awkwardly bumping his head against the locker in embarrassment before he left for class.
In Dreamcatchers, Hayden and Liam were in Mr. Yukimura's class at school several days later when Hayden noticed Tracy Stewart, the newly-turned Kanima-Werewolf Chimera Tracy Stewart, who was suffering from night terrors and hallucinations caused by the Dread Doctors' experimentation, sitting next to her; this revelation confused Hayden, who was alarmed by the fact that Tracy was dirty, disheveled, barefoot, and clutching the desktop so hard with her clawed hands that it snapped in half, and was also concerned by the fact that Tracy, as a senior, had no reason to be in a sophomore-level history class.
Liam, who also noticed that Tracy was in the class and knew that the McCall Pack had been searching for her to help her, left the room to pull the fire alarm to give them a chance to sneak Tracy out without anyone noticing, leaving Hayden to try to calm her down. However, when Hayden gently encouraged her to come with her, Tracy grabbed her by the wrist and squeezed it so hard that her claws sliced her skin. Scott and Liam returned to try to talk Tracy into coming with them until Tracy finally let go of Hayden, and the three watched in horror as Tracy muttered, "They're coming. They're coming for all of us" before throwing up a large puddle of modified mercury and passing out onto the floor.
Once Scott, Stiles and Malia managed to sneak the unconscious Tracy out of the school so they could take her to the animal clinic to be assessed by Alan Deaton, Liam stayed behind and asked Hayden, who was clutching her bleeding wrist, if she needed help getting to the nurse's office. Hayden, still holding a grudge for what happened in the sixth grade, snidely retorted that she could manage it herself and walked away. Despite claiming she was going to the nurse's office, Hayden instead went to the girl's restroom to clean up the wounds herself, which was where she found to her horror that the claw gashes Tracy caused from squeezing her wrist had completely healed in only a few minutes.
In Condition Terminal, Hayden was at work as a server at the new nightclub Sinema when she approached by Liam and Mason. She snidely reminded Mason that she promised him entry into the club with a plus-one, not a "plus-Liam," but when Mason offered her fifty dollars, she reluctantly allowed both of them entry. While they were there, Liam's superhuman Werewolf senses caused Liam to get the impression that there was a malicious supernatural creature at the club, distracting him so much that he accidentally ran into Hayden. Hayden then subsequently dropped her tray of body shots onto the ground as a result of the impact and instantly became furious at Liam before reminding him that each shot was ten dollars and that they would all be coming out of her paycheck. Liam began to apologize profusely as he dug around his pockets for money to pay her for the spilled drinks, but all he had was twelve dollars and some change, which Hayden took before angrily informing him that he still owed her $200 and throwing the coins at him as she walked away.
In Required Reading, Liam, still feeling guilty about the money he owed Hayden for spilling the tray of drinks, went to Sinema to find her and give her the forty-three dollars he had scrounged up as a down-payment on his debt. However, Hayden insisted that she didn't want it, and when Liam reminded her this in addition to the money he had already given her was only fifty-five dollars out of the two hundred he owed her, the power went out in the club, killing both the lights and the music in the process.
The club-goers started to boo and groan at the interruption, forcing the overwhelmed Hayden to have to go out the back door of Sinema to turn on the back-up generator. Liam followed after her and continued to insist that she take his money, but Hayden stated that his attempts to be a "good guy" weren't working on her. When she turned away from him to try to turn on the generator, she began to struggle with the lever to the machine until Liam came up behind her and used his Werewolf strength to help her lift it. He then looked her in the eye and told her that it was okay if she wanted to hate him, but that since he owed her money, she should take what he was offering, which Hayden reluctantly did.
The next day, Liam and Hayden were in gym class together, where the girls were practicing soccer on one side of the field while the boys practiced lacrosse on the other. When Hayden realized Liam was trying to show off his skills to impress her, her competitive nature kicked in, and she began kicking perfect goals to outshine him. The more determined Liam grew in an attempt to beat her, the worse his attempts to make a goal became until he finally made a shot with so much strength that he hit the goalie in the chest and knocked him backward. Meanwhile, Mason and Brett Talbot were sitting in the bleachers, where Mason explained how Hayden and Liam's rivalry began; Liam was in a violent fight with a fellow student in sixth grade when Hayden came out in the hall to see what was going on, causing Liam to accidentally punch her in the face and break her nose. Hayden, furious at Liam for breaking her nose right before yearbook photos, punched Liam in the face in retaliation, causing them both to have broken noses that day.
Suddenly, another student ran onto the field to ask if anyone had an inhaler, leading Liam to realize that his close friend and Alpha, Scott, was having an asthma attack. After Liam ran into Mrs. Finch's classroom to help Scott, Hayden followed after him and was impressed by how Liam did not hesitate in trying to help his friend, which caused her to rethink her preconceptions of him. After school, Hayden's sister, Valerie Clark, stopped by to drop off Hayden's medication, which Valerie said almost got run through the washing machine after Hayden left the bottle in her pocket. Liam walked past them just in time to overhear Valerie mention that the medication cost $200, which led Hayden to make a snarky comment to Liam staring at her. Liam insisted he wasn't looking at anyone and kept walking, though he smirked to himself when he overheard Valerie state that he had gotten cute since he and Hayden were kids.
That night, Liam stopped by Sinema before it opened to give Hayden another twenty-five dollars. Hayden, now touched by the lengths Liam has been willing to go to make things right, assured him that it was okay. Liam reminded her that he promised to pay her back, but Hayden told him that it didn't matter now, especially since her boss, Phil, takes half of her paycheck anyway. When Hayden returned to set up candles for when the club opened, Liam awkwardly blurted out that he knew that she meant to use the $200 to pay for her medication and begged her to take it, but Hayden just laughed and told him it wasn't his fault. Liam argued that he punched her in the face, but Hayden pointed out that she was talking about the spilled shots before she revealed that the medication was mycophenolate, an anti-rejection medication she has had to take since she had a kidney transplant several years earlier.
She went on to say that she works at Sinema so that her sister won't have to pay for all of it herself and insisted that Liam shouldn't worry about it, as she would figure out a way to make up for it herself. When Liam asked her if her boss, Phil, really took half of her paycheck, Hayden chuckled and confirmed that he did before informing him that he was bragging about it as they spoke and that Liam should listen for himself. Liam focused his Werewolf hearing to listen to Phil's conversation with a potential hire before realizing that there was no way Hayden could hear it with normal human senses.
He frowned anxiously before asking her to close her eyes as a favor to him. Hayden, feeling uncomfortable with the question, initially rejected his request, but after he convinced her that it would only be for a few seconds, she eventually relented and did as she was asked. Liam then took a nearby glows-tick and broke it, causing it to glow brightly before he held it up in front of Hayden's face and asked her to open her eyes. When she did so, he was horrified to see that her eyes were reflecting the teal light of the glow-stick back at him, indicating that Hayden had been turned into a Chimera by the Dread Doctors.
In Strange Frequencies, Liam followed Hayden out into Sinema's parking lot after his failed attempt to both reveal the existence of the supernatural world (including the presence of the Dread Doctors in Beacon Hills) as well as his secret identity as a Werewolf. However, Hayden, believing that Liam was just messing with her, rushed away from him, ranting about how weird it was that he asked her to close her eyes before sticking a glow-stick in her face and demanding that he get away from her. When Liam asked her if she would allow him to prove it to her, she responded with confusion as Liam partially transformed, revealing his fangs and gold glowing eyes and roaring in her face. The now-frightened Hayden yelped and reflexively punched him in the nose so hard that he not only got a bloody nose, but he was also knocked flat on his back on the pavement.
Hayden quickly got into her car and sped away, driving on the back road near the Beacon Hills Preserve for a short while before pulling over to calm down. She winced when she realized she had hurt her knuckles when she punched Liam, but just as she was about to evaluate the damage, her fist healed itself within seconds, shocking her. Before she could think about this further, the radio in her car started to tune itself as robotic voices began to call her name through it, stating that her condition was improving and confirming her status as a Chimera.
When she saw the Dread Doctors slowly marching toward her, she began to panic as she tried to turn her car back on to drive away. Unfortunately for her, the Doctors were using their electromagnetokinetic powers to prevent her car from starting as well as to lock the doors so she could not escape. Moments later, Hayden was scared by the sound of someone punching through her moon roof until she realized it was Liam coming to rescue her. He reached his hand toward her for her to take and helped her crawl out of the car before the two ran in the opposite direction of the Dread Doctors.
Later on, Scott and Stiles, who were called by Liam, returned to the McCall Pack to find an anxious Liam. Liam briefly explained what happened before informing them that, while Hayden seemed fine when they arrived at the house, she suddenly freaked out and locked herself in Scott's bathroom. Scott and Stiles tried their best to coax her out, with Scott assuring her that they just wanted to help her and Stiles reminding her that her sister Valerie works with his father Noah Stilinski at the Beacon County Sheriff's Station.
When this proved ineffective, Scott finally stated that he needed to get into the bathroom to make sure she was okay, and that if she didn't want to talk or wasn't ready to learn the truth, that was okay. Just as Scott was about to break the door open, Hayden unlocked it and allowed it to open itself, revealing to Liam, Scott and Stiles that she had locked herself in due to the fact that she had lost control and partially-transformed-- her nails extended into claws, her teeth extended into fangs, and her eyes glowed gold just like a Beta Werewolf, revealing that she was a part-Werewolf Chimera.
Knowing that the Dread Doctors would try to capture Hayden again to continue their experiments, Liam, with the help of Scott, Stiles, Malia, Lydia and Parrish to create a trap for the Doctors in Beacon Hills High School, as they believed they could use frequency jammers in conjunction with the powerful convergence of telluric currents running through the location to protect Hayden. However, unbeknownst to Hayden and Liam at the time, Hayden was also being used as bait in the hopes that the McCall Pack might have enough luck to catch a Doctor to question it on their plans. While Liam and Hayden hid with Scott and Lydia in the locker room, Malia and Parrish stood watch in the entrance hall and the front of the school, respectively.
Upon seeing Hayden staring at herself in the mirror with a concerned expression, Liam assured her that she would learn to control her new powers. When Hayden replied that she wasn't like him, as she was the Dread Doctors' "science experiment" rather than being bitten by an Alpha Werewolf, Liam promised that she would be okay. Hayden, who was clearly developing requited feelings for Liam, smiled and informed him that if he could get her out of this situation, she would forget all about their fight in the sixth grade. As time passed, Hayden and Liam sat on the floor, leaning against a row of lockers, where Hayden nuzzled her head into Liam's shoulder and tried to sleep, a level of affection that surprised Liam.
However, when Liam saw a bag nearby, his curiosity won over the effects of his crush, and he wandered over to find that the bag was full of chains, forcing Scott to admit his intention to try to capture one of the Dread Doctors if it came to it. This led to an intense argument between Scott and Liam regarding the use of Hayden as bait, and when Scott had an uncharacteristically frustrated outburst, Liam, knowing that they had no other choice, made Scott promise to do anything he could to save Hayden. Just then, Hayden realized that she forgot her anti-rejection medication and that she needed to go to her locker to get it, Scott offered to go get it for her.
The fact that they were all separated for the moment ultimately allowed the Dread Doctors to use their electromagnetokinetic powers to manipulate their minds by inducing hallucinations in everyone except for Liam and Hayden. When Scott, Lydia, Malia, and Parrish were all incapacitated by these hallucinations, the two attempted to use the frequency jammers to stop the Dread Doctors. Unfortunately, these did not even slow them down, and The Surgeon stomped on the jammers, stating that they exist on a frequency that they couldn't imagine before capturing them both and bringing them back to the Dread Doctors Operating Theater. When Liam woke up on the floor of the operating theater, he found that he was hooked up to an IV of black fluid being pumped into the crook of his elbow while Hayden was strapped face-down to an operating table while the Dread Doctors performed surgery on her back.
In Ouroboros, Hayden and Liam were both still being held hostage by the Dread Doctors. Liam once again awakened to find the Doctors performing experimental procedures on Hayden, who is pale and covered in sweat. Suddenly, a loud alarm went off, causing The Pathologist to walk over to the tank full of green serum and a body with an oxygen mask and draw up some of the fluid into a large syringe. Liam, still flat on his back on the floor with a large IV full of black Wolfsbane goo, watched as the Dread Doctors took a UV light and ran it over the skin on the back of Hayden's neck, revealing what almost appears to be jaguar spots under her skin. The Surgeon stated that Hayden's "condition worsens," and Liam, horrified, screamed at them to leave her alone, only for the leader of the Dread Doctors to kick him in the face.
Some time later, once the Dread Doctors had finished their procedures on Hayden, they threw her down on the ground next to Liam, who crawled over to her to see if she was all right. The surgical wound they made on her side was shown to be seeping blackened blood, and it was clear that Hayden was in a lot of pain. Liam pointed out that he had seen Scott use his Werewolf powers to take the pain of others and took Hayden's hand in hopes of doing the same. However, despite Liam focusing all of his energy into successfully performing this feat, he's unable to alleviate her pain, and Hayden weakly let go of Liam's hand in order to apply pressure to her bleeding wound.
After some time passed, Hayden and Liam managed to get into a seated position, where Hayden was assisting Liam in removing the large IV tube in his right arm. Despite the pain it was causing him, Liam insisted that she continue to pull on the tube until it finally comes out, gushing black Wolfsbane solution all over them. Before they can share a relieved look, the Dread Doctors appear and put them both in head-locks so they can inject them in the neck with a tranquilizer of some sort.
When the two awaken from their stupor, they find that they are no longer in the Dread Doctors Operating Theater, but instead the Abandoned House that the Doctors were using as a holding cell for the Chimeras who were no longer needing experimentation but who were not yet ready to return to regular life. Liam, seeing the room was enclosed with a chain-link fence, rushed over to try to rip them a tunnel to escape, only to be badly electrocuted the moment that his fingers touched the metal.
It was then that Hayden and Liam realized they weren't alone, and that they had a fellow Chimera cellmate named Zach, who asked if they would look at his back, because he knew the Doctors had removed something but he could still feel part of it back there. When he raises the back of his shirt, they're shocked to find two little nubs that twitched like hummingbird wings, suggesting that he had wings before the Dread Doctors surgically removed them.
Zach went on to laugh when Liam once again tried to escape through the electrified fence and grimly stated that they were never getting out. When Hayden reminded him that optimism never hurt anyone, Zach retorted that it was hard to remain positive when he's seen three other Chimeras dragged out of the cell and killed, adding that the Dread Doctors referred to them as "failures." According to Zach, a "failure" was typically identified by certain traits-- first, they forget who they are or what they're doing, then they become feral and violent as they succumb to their hallucinations. He went on to say that one of them had a "nasty cut" just like the one Hayden had on her side, but he reassured her that black blood wasn't a bad sign, adding that "it's not really over" until a Chimera began bleeding Modified Mercury.
Some time later, Liam and Hayden looked horrified when Zach suddenly starts to bleed mercury from his nose, and they fled to the nearby corner when the Dread Doctors arrived to take him out of the cell, presumably to kill him for being a failure. Once hours had passed, Hayden and Liam heard footsteps and assumed they were from the Doctors, holding each other's hands in preparation for a fight. However, it was actually Theo, who had arrived to save them and who grabbed the fence to open it before they could tell him that it was electrified. Theo was thrown backward by the force of the electricity, but despite it, he tried a second time to open the gate, ultimately "wolfing-out" enough to withstand the electricity and free Hayden and Liam from their captivity.
As Theo drove Hayden and Liam back to the McCall House, Hayden noted that the wound on her side still wasn't healing and that she believed she was a failure like the others. Liam, not knowing what else to do, kissed her and inadvertently absorbed all of her pain, not realizing what he had done until Hayden informed him. The two kissed again while Theo watched them from the driver's seat. Hayden and Liam were then seen again at Scott's house, where they had fallen asleep on his couch and were covered up with a blanket by Lydia.
In Lies of Omission, Liam, who has been checking up on Hayden in every hour, starts becoming worried when Hayden starts bleeding Mercury they decide to run away together but it is too late and the Dread Doctors find them Hayden is injected with something and Liam wants Scott to give her the bite to save her.
In Status Asthmaticus, Liam standing by a dying Hayden's side, Start worrying when she becomes weaker, Liam goes after Scott to gain his power and give Hayden the bite unfortunately Hayden dies and Liam goes to hold a dead Hayden his arms and Parrish come to collect her Liam give's her a kiss on the cheek goodbye and cries as he watches Parish walk away with her.