Erica is in the same gym class as Scott, Stiles, and Allison. They're doing a rock wall, but Erica only gets part of the way up before she freezes in fear. She's humiliated at having to be lowered back to the ground without making it all the way. Tired of being unable to do things that everyone else can do, she resolves to climb the wall no matter what. After class is over, Erica starts climbing without a safety rope. Scott senses her seizure coming on and runs out into the gym in time to catch her as she falls. She is taken to the ER, where she's looked after by Mrs. McCall.
While Erica is in the hospital, Derek arrives and wheels her into the morgue. He uses his sex appeal to convince her that he can make her problems go away. He tells her that her seizures can be cured if she accepts the Bite. She agrees and becomes the second member of Derek's Pack.
The next day, Erica comes to school having gotten a complete makeover. She goes to the lunchroom so everyone can see the new her, steals someone's apple, and then leaves, having made her point. Scott and Stiles follow her out and watch her get into Derek's Camaro. Derek grins at them and drives off. During school the next day, Scott approaches Erica and asks her who Derek has planned to turn next. She doesn't answer him, instead explaining why she chose to get the Bite: people at school once recorded her having a seizure and pissing herself and then posted it on YouTube to humiliate her. She didn't want to be that vulnerable anymore.
Scott and Stiles figure out that the next person is going to be Boyd, and Erica follows Stiles to Boyd's house. She uses her sexuality to distract him and then hits him over the head with a car part. Erica puts Stiles in a Dumpster and goes back to meet up with Derek and Isaac. The three of them find Scott and Boyd at the skating rink. Derek tells Erica and Isaac to attack Scott, but he beats the both of them.
After their poor performance, Derek starts fight training sessions in the subway hideout for Erica and Isaac. They don't seem to learn much, and he gets tired of continually slamming them into the ground. Frustrated, Derek asks if someone will do something not completely predictable, at which point Erica leaps up and kisses him. He kisses her back for a little bit before throwing her off and telling her never to do that again. He wants her to come onto Scott instead.
The next day, Erica and Boyd attend a lacrosse game. Boyd gets pulled out of the stands to play, and while he's gone, Erica follows Stiles into the principal's office and then drags him to meet Derek at the pool. Derek demands to know everything Stiles knows about the reptile creature that's killing people. As Stiles describes it, the creature crawls down from the ceiling. Erica tries to attack it, but it quickly either knocks her out or poisons her with paralytic toxin. Erica doesn't reappear until after Scott has come to the rescue. She stands with Derek as he explains that the creature is a kanima and an abomination. Derek and Erica leave with Derek vowing to kill the creature.
Since Jackson is the most likely candidate to be the kanima, Derek sends Erica to get him. She finds Jackson in the boys locker room trying to lift too much weight on the benchpress. The bar is crushing his chest, but Erica lifts it up with one hand. She brings Jackson to the subway hideout and then she and Isaac hold him while Derek puts a drop of venom in Jackson's mouth. It paralyzes him, so they assume he can't be the kanima. They make Jackson promise to recant his testimony about Isaac and his father fighting on the night of Mr. Lahey's death, which exonerates Isaac and lets him return to school.
Both Erica and Isaac are supposed to administer the same test they did on Jackson to Lydia, the next best candidate because she got the Bite but didn't turn. In Chemistry class, Mr. Harris announces that they will be doing a group experiment. He calls on Erica first, and everyone in the classes raises their hand to be her partner. Mr. Harris deadpans that he didn't ask for a volunteer. Erica gets paired with Scott first. She tries to come onto him, sliding her hand up his thigh, but he shuts her down, and she realizes that Scott and Allison are still an item. Mr. Harris rings the bell for everyone to switch, and after two shifts Erica is sitting with Allison. Allison asks her what they're planning to do, but Erica replies that they should be more concerned with what Lydia will do. She then tells Allison that she's always thought of herself as a little psychic and predicts that Allison and Scott won't last. Allison asks her if she thinks putting her hand on Scott's thigh is really going to do anything, so Erica puts her claws on Allison's thigh and asks if she wants a girl fight in the lab. She dig her claws in a little, and Allison jumps.
Mr. Harris rings the bell again, and the experiment is done. Isaac gives Lydia the venom on the sugar crystal they should have created. Lydia fails the test, so Isaac and Erica have orders to kill Lydia. During the next period, the two of them flounce down the hallway toward the library, where they expect to find Lydia. When it's clear she's not there, they join up with Derek and go to Scott's house. Isaac goes into the house first and attacks Allison and Stiles. Erica goes in and finds Allison in Scott's room. Allison fires a crossbow bolt at her, but Erica catches it. This is actually what Allison was hoping for, because she rolled the bolt in kanima venom first. Erica falls down paralyzed, and Allison taunts her. "I thought you were psychic, bitch."
When Scott arrives, he tosses both Isaac and Erica out of his house. Derek orders Boyd to get them in the car.
A few days later, Erica, Isaac, and Derek talk about their next steps. Derek wants Erica to get close to either Scott or Stiles because he thinks they know more about the kanima. Isaac is concerned about all of them being chained up during the full moon, because it will leave Derek on his own. He wants to forget about the kanima and focus their energies on the Argents, but Derek says they can't because Gerard wasn't afraid of the kanima so he must have some plan up his sleeve.
The next school day, Erica catches Stiles pestering Lydia with questions about Jackson's birth parents. She slams him up against a wall and demands to know why he wants to know. Stiles suggests she not bring out the claws where the school's new security cameras can see. Erica tells him that Jackson's birth parents are dead. She walks away, and Stiles follows her, trying to find out what else she knows about his birth parents. His interest convinces Erica that Jackson must be the kanima. Stiles begs Erica to stop trying to kill people. He insists that getting a Werewolf makeover is not license to hurt others. She retorts that that's all anyone ever did to her. She admits to having a crush on Stiles but he never even noticed her. She complains that he's not paying attention to her now, but it's because there's water coming out of the boys locker room. Scott comes flying out the door with Jackson soon after. Mr. Harris sends everyone in the hallway to detention.
At detention Erica tells Stiles that her father was the insurance investigator on Jackson's parents' car accident. She pulls up her father's email and checks the accident and insurance reports. Jackson's parents both died in a car accident on June 14. Jackson was born on June 15, meaning he was pulled from his mother's dead body. Mr. Harris eventually leaves and tells everyone that they can leave when they shelve all the library books. While they're working, Jackson turns into the kanima and attacks everyone. He poisons Matt and Erica, and Erica starts having a seizure. It's not exactly the same as her epileptic seizures, but they need to do something to help her. Stiles and Scott want to take her to the hospital, but she insists on being taken to Derek.
Derek is visibly shaken at seeing a werewolf have a seizure. He breaks Erica's arm to boost her healing and then squeezes her arm to try to get the toxin out of her system. Erica leans against Stiles and tells him he's a good Batman. Stiles stays with her in the subway car when Derek and Scott go to talk. Scott joins Derek's pack to help stop Jackson.
The new plan is to capture Jackson at the rave on Friday night. Stiles will surround the building with mountain ash, while Scott, Isaac, and Erica knock Jackson out with ketamine. Their hope is that the kanima's master will be stuck inside the mountain ash just like kanima is. Once inside the rave, Erica and Isaac dance with Jackson to distract him. Isaac is almost able to stick him with the needle, but the kanima's master figures out what they're doing and has him stab them both with his claws. Isaac recovers quickly enough to attack Jackson from behind, inject him, and haul him away. He, Erica, and Stiles lock Jackson in a small room. Erica watches as Isaac goes to test how out of it Jackson is and gets his wrist broken in the process. It quickly becomes clear that Jackson is unaffected by the ketamine and begins to shift. The three of them scramble outside, and the kanima bursts through the wall to escape.
Erica and Isaac run over to where Derek and Stiles stand by the mountain ash line. Stiles realizes that they can't pass it and cheers. Derek tells him to break the line because he can hear Scott dying.
They all retreat to the subway hideout. Wednesday night is the night of the full moon, and Derek needs to chain all the betas up. He tells them that they're going to want to kill him and every other living thing they can find. Erica quips that it's a good thing she had her period last week. Derek tries not to smile at that. He shows her the headband that she'll get to wear. He gets them all inside the subway car and chains up Erica first. Because she can withstand the most pain, she needs the headband as extra restraint. Derek asks her if she's ready and then starts screwing the bolts of the band into her skull. She screams.
Despite the extra chains, Erica is still able to break out once the full moon rises. She attacks Derek, and is quickly aided by Boyd. Once Isaac gains control of himself, he helps hold Boyd down while Derek chains Erica back up again.
After the death of Allison's mom, the Argents are hunting Werewolf with new vengeance. Boyd and Erica are scared and pretty sure they're going to die, so they tell Derek they want to leave and find a new pack. While they were out in the woods, they heard wolves howling and assumed it was another werewolf pack. Erica tells Derek that she wants to live to get her driver's license. He tells them that if they start running now they won't ever stop. They declare that they're leaving anyway, and Erica takes Boyd's hand to lead him out.
They go in search of the howling that they heard, but it quickly becomes clear that it was the Argents laying a trap. Erica and Boyd try to run from the hunters on ATVs, but eventually Allison gets a clear shot and shoots Erica in the leg. Erica falls but tells Boyd to keep running. It looks like he does, but he comes back and saves her from taking an arrow to the face. While Allison fills Boyd full of arrows, Erica cries and screams at her to stop.
The two of them get taken hostage and strung up in the Argents' basement. Their bonds are electrified to keep them from escaping. The only person who knows that they've been captured is Stiles, when Gerard abducts him from the lacrosse game and beats him up as a warning to Scott. Chris Argent comes down to visit them and explains how his family knows a lot of about the ways electricity can affect Werewolf, but he doesn't turn the power up to hurt them more because he's convinced that Gerard is a bigger threat than they are.
After Gerard is stopped and Jackson saved, Boyd and Erica are released. They're again running through the woods, only this time they get captured by a group of Werewolf, which turns out to be an alpha pack.