Jackson and Danny are in the boys locker room without the lights on. Jackson tells Danny to add more weight to the benchpress bar and then gets angry at him when Danny spots him. Jackson thinks he should be able to benchpress twice the amount that's on there. "On the moon, maybe," Danny replies. He leaves, annoyed, and tells Jackson that if he finds him dead when he comes back from his shower he's taking the Porsche. As he lays there, Jackson's senses start to sharpen, and he can hear water dropping and the turn of the fan blades better than he should be able to. He's not satisfied with that, though, and tries to lift the bar with too much weight. It goes right down to his chest, and he can't lift it. Erica appears over him and lifts the bar from his chest with one hand.
Erica delivers Jackson to Derek in the subway tunnel. She and Isaac hold him, while Derek asks him what happened to him on the night of the full moon. Jackson claims nothing happened, but Derek can tell he's lying. Derek starts to put on a black leather glove, and Jackson freaks out a little. He tells him that he can prove it and says that he taped himself. Derek and Isaac find this amusing. Jackson makes fun of Isaac for having an existential crisis and says the he was preparing for the gift Derek promised. He tells him he'll get the video, even though he knows that the video is missing two hours of footage. Derek picks up the piece of broken mirror that Scott used against the kanima and claims that he has a better idea. "You know, Jackson, you've always been kind of a snake. And everyone knows a snake can't be poisoned by its own venom." Derek then tips the glass toward Jackson's mouth. Erica and Isaac hold his jaw open, so he swallows a drop of the kanima toxin. The effect is immediate, and Derek is clearly disappointed that Jackson passed the test. While Jackson is on the floor, unable to move, Isaac comes over and crouches in front of him. "You're still gonna have to do one more thing for us. Well, actually, for me."
4Isaac makes Jackson go to Sheriff Stilinski and retract his statement about seeing them argue before Mr. Lahey was killed. The Sheriff asks him if he saw a fight, and Jackson tells him, "Not exactly." The Sheriff explains that in law enforcement there's a very large divide between "not exactly" and "no." "Like if Not Exactly were sitting in this chair, then No would be somewhere in the middle of the Pacific Ocean drowning next to my career."
Stiles comes running into class to tell Scott that he has real terrible horrible very very bad news. Scott motions to Isaac sitting a few desks away. "I think I already know." Isaac looks smug, while Scott and Stiles look stressed. After class, Stiles reports that the only thing he could find about a kanima was that it was a werejaguar from South America that goes after murderers. Scott points out that the thing they saw was not a werejaguar. Stiles points out that he is not a murderer. Scott waxes on how it'll probably keep coming after Stiles until he's dead, much to Stiles's dismay. Danny tells Jackson that he found a program that could recover the erased data from his video. He says he'll run it during their free period that afternoon. Jackson then overhears Erica talking to Isaac, confirming that Derek wants something done during Chemistry class. Isaac advocates just killing their target, while Erica says she's going to test her first.
In Economics class at 1:45, Jackson sits near Scott and Stiles. "Hey, testicle left and right, what the hell is a kanima?" The boys turn around, but before they can say anything Coach Finstock announces that some of them might want to form study groups for tomorrow's midterm. Jackson tells Scott and Stiles that Derek tested him to see if he was the kanima. Stiles then asks if they think it's Lydia. Jackson isn't sure, he just heard her name and something about Chemistry. Coach Finstock shouts at Jackson and asks if he has something he'd like to share with the rest of the class. Jackson compliments the Coach, and Finstock yells at him to shut it. Scott asks Stiles how he knows the kanima isn't Lydia. "Because I looked into the eyes of that thing, okay? And what I saw was pure evil. And when I look into Lydia's eyes, I only see 50% evil. All right, maybe 60." Scott points out that that's not a good argument, and Stiles is aware of that. "Lydia's fine," he says. As she's watching a student at the board, Lydia sees him change into Peter Hale. The writing on the board is in a revenge spiral. Everyone is staring at her. Then suddenly all the students are gone, and Peter turns around to face her. He throws desks across the room as he comes at her, and she jumps up with a cry and backs against the wall. Peter walks up to her, crushing something in his hand, and then blows a white powder in her face. Lydia comes out of her vision crying, with Coach Finstock calling her name. She's up at the front of the room, and she's written ɘmqlɘʜɘnoɘmoƨ (Someone Help Me) all over the board. Young Peter Hale is seen sitting in the class just a few desks away from Stiles. Finstock asks if someone would like to try answering in English, and everyone laughs. Scott asks if it's Greek. Stiles shows him a photo he just took of the board and flips it, revealing that it's English, just mirrored.
Stiles and Scott head into Chemistry. Scott is sure that Derek isn't going to just kill Lydia without proof. Stiles asks when and where. When they see Erica and Isaac come into the room, they realize that the test is going to happen right then. Scott quickly takes the empty seat next to Lydia. Stiles sits next to her on the other side, even though there isn't an empty seat there. Allison comes in, and Scott motions for her to be wary of Erica and Isaac. Mr. Harris quotes Einstein as saying that two things are infinite, the universe and human stupidity, and "I'm not sure about the universe". He then claims to have seen his own share of stupidity and pats Stiles on the back. Stiles gets perfect grades, so his insult, while generally uncalled for from any teacher, is extra out of place directed at Stiles. Harris says they are going to conduct some group experiments. "Let's see if two heads are indeed better than one. Or in Mr. Stilinski's case, less than one." He tells Erica to take the first station, and nearly all of the people in the room raise their hand to be her partner, even though Harris didn't ask for volunteers. Harris pairs Erica with Scott. Scott pours some blue liquid into a beaker and asks Erica to wait before she does whatever she's planning. Erica tells him to talk to her instead and leans in close, but Scott pulls away. Erica can smell Allison all over Scott and realizes they aren't as broken up as they try to appear. She puts her hand on his leg and tells him that she'd be wanting him all the time. Lydia sees Erica touching him and asks Allison if it's true that she never gets jealous. Allison acts nonplussed. Scott tries to take Erica's hand away, but she gets rough with him. Just then Harris rings the bell and tells them to switch stations.
Allison advises Lydia to not talk to Erica or Isaac. Everyone switches, and Scott takes the seat next to Lydia. Stiles is with Isaac. "If you harm one perfect strawberry blond hair on her head, I'm gonna turn your little werewolf ass into a fur coat and give it to her as a birthday present," Stiles tells him. Isaac isn't amused. He tells Stiles that he did ask Lydia out once, the first day of freshman year. They talk about how she spited him. Stiles suggests channeling all his negative energy into writing in English class. "Nah. I was thinking I'd channel it into killing her. I'm not very good at writing." Harris rings the bell for them to switch again, and this time Isaac sits next to Lydia. Stiles tries to get up to intervene, but Harris slaps him with a pointer. Allison is sitting next to Erica and asks what they're planning to do. Erica tells her that the better question is what is Lydia going to do to all of them. She then says that Allison and Scott are cute together but she doesn't think it's going to last. Allison counters by asking if she thinks she can hurt her by sliding her hand up Scott's thigh. Erica then puts her claws on Allison's thigh and asks if she wants to have a girl fight in the lab. She digs her claws in, and Allison reacts in pain but doesn't make a sound. Harris rings the bell and announces that if they've done the experiment correctly they should have a crystal that they can eat. Stiles and Scott have a beaker of beige goo. Isaac offers Lydia the crystal with a drop of kanima venom on it. Scott sees the drop and jumps up to tell her to stop, but he's too late and the drop doesn't seem to affect her, so he sits down. Lydia eats the crystal and shows no signs of being paralyzed. Scott sees Derek out in the parking lot awaiting the results.
Stiles, Scott, and Allison meet in Finstock's office. Scott says that Derek is waiting outside to kill Lydia. Stiles insists that it isn't her. Allison points out that it doesn't matter what the truth is, if Derek thinks Lydia's the one, they either have to convince him otherwise or find a way to protect her. Scott doesn't think the attack will happen at the school. Allison suggests that there's something in the bestiary that could help, but Stiles points out that it's a 900-page book in archaic Latin that none of them can read. Allison thinks she knows someone who can translate it. Scott offers to talk to Derek to try to buy them time. He asks that they not put themselves in harm's way because he can heal faster than they can. Allison doesn't like being talked down to that way and produces a hand-held crossbow from her bag. Scott gives her a long, sad look and insists that he doesn't want her getting hurt. He tells her that if anything goes wrong to call him or text him or scream and yell, whatever it takes. He'll hear her and find her as fast as he can, and he doesn't care if her dad finds out. As Scott turns to leave, there's the twang of a bow, and Scott spins around to catch a bolt before it hits him the back of the head. Stiles had been messing with the crossbow.
Lydia is back at the guidance counselor's office. Ms. Morell holds up a series or Rorschach tests and Lydia says that they're all butterflies. The final one, however, looks to her like Peter's burned, bloody head. Ms. Morell asks her what it will take to get her to open up, and Lydia replies that she's as honest and open as a person can be.
In the library, Matt comes up to Danny and Jackson and asks Jackson who he knows that could get into his house. Either someone who could break in or has a key. "I could do it," Danny offers. "I write my own software, and I know your mom forgets to lock the kitchen door." Matt claims he could have done it because it's his camera. He then smiles at Danny and suggests they could have done it together, which makes Danny smile. They seem to be flirting a little. Matt leaves and pats Danny on the shoulder. Jackson gives him a look like he knows that was flirting. Danny tells him that it doesn't matter because Matt is completely obsessed with Allison. Danny asks if anyone can get into Jackson's house, and just then Lydia and Stiles walk into the library. Jackson realizes that it could be Lydia because she has a key.
Allison brings Ms. Morell a page from the bestiary to see if she can read it. Ms. Morell translates: Like the wolf, its power is greatest at the moon's peak. Ms. Morell tries to get out of reading more, but Allison begs her to try to translate it now. Like the wolf, the kanima is a social creature, but where the wolf seeks a pack the kanima seeks a friend. Allison asks what a friend could mean, and Ms. Morell suggests that maybe the kanima is lonely.
Scott goes out the lacrosse field and meets with Boyd. He says he wants to talk with Derek and doesn't want to fight. Boyd tells him that's good because he's twice his size. Scott admits that that's true but he thinks he's twice as fast and tackles Boyd to prove it. Derek shows up and says that Lydia failed the test. Scott tells him that he's not going to let Derek kill Lydia, and Derek replies, "Who said I was going to do it?" Scott then realizes that he's in the wrong place. Isaac and Erica flounce down the hallway of the high school. Isaac runs his claws along the lockers, scratching off paint and causing sparks.
Scott tries to run for the school, but Boyd clotheslines him. Derek says that he isn't sure why Scott feels like he has to protect everyone, but Lydia is dangerous and going to kill more people. Lydia was bitten by an alpha, which in Derek's mind means it has to be her. "You saw that thing up close. You know it isn't like us." "But it is. We're all shapeshifters." Derek tells him that it's rare but sometimes the shape you take reflects the type of person you are. Scott suggests that Lydia could be immune. Derek tells him that no one is immune. He's never seen or heard of someone being immune to the Bite. "It's never happened!" "What about Jackson?" Derek doesn't have an answer for that.
Back in the library, Matt looks at his photos from the game and sees lens flare any time he took a photo of Scott.
Scott accuses Derek of testing Jackson because he gave him the Bite and it didn't either kill him or turn him. He says that he thinks Lydia is immune and passed that on to Jackson. Derek doesn't believe it. Scott tells him that he was hoping he could convince him not to kill her but he wasn't counting on it.
Isaac and Erica head into the library looking for Lydia. Isaac grabs Matt and demands to know where "she" is. Meanwhile, Stiles, Lydia, Jackson, and Allison head out of the library for a study group. They all get into Stiles's Jeep and drive away.
Scott runs into the school and it stopped by Coach Finstock who wants to know why there is lacrosse gear that's destroyed. Someone found Danny's gear under the bleachers. Finstock tells him to make sure Danny takes care of his equipment or Scott will be responsible for it. "Do you want to be responsible for taking care of Danny's equipment all the time?" "That depends, are we still talking about lacrosse pads?" Because apparently if they weren't, Scott's answer would differ?
Stiles, Lydia, Jackson, and Allison go to Scott's house. Allison thanks Jackson for helping, but he says he needed to talk to Lydia anyway. When they get inside, Stiles locks every lock on the door and explains that there's been a few break-ins around the neighborhood. Allison motions to Jackson, and Jackson asks Lydia to follow him to he can talk to her.
Back at the high school, class lets out. Scott runs into Matt, who turns and takes a picture of him. The photo again has lens flare.
Jackson and Lydia go up to Scott's room, and Jackson starts getting a headache. He asks Lydia for his key back. She yells at him for his insensitivity, but he just asks for the key again. She says she doesn't have it, but he can see her sweat and hear her heart.
Scott confronts Danny in the library with the ripped up pads. Danny asks him what he did to them, but Scott asks him what happened. Danny says he was playing goalie, which has a different set of pads.
Allison calls Scott from Stiles's phone and tells him to get to the house. Derek and the betas are outside.
While Danny is looking at his destroyed pads, his computer finishes the video reconstruction. It shows Jackson starting to sit up while still asleep. He opens his eyes, and they are completely yellow.
Allison doesn't want to, but she thinks she has to call her dad. The situation is too dire, even if it costs her her relationship with Scott. Upstairs, Jackson accuses Lydia of editing the tape. He says he doesn't know why she would do that. Maybe she wanted to take his moment like she takes everything. She tells him that if he wants the key so badly he can have it, and then removes the chain she keeps it on from around her neck. She cries, and he can't quite stand it, so he kisses her.
Stiles tells Allison to shoot one of the betas. They told Scott they could protect themselves, so they should step up. Stiles thinks that the Werewolf aren't expecting a fight, so if they get one they'll leave. Allison asks which one, and Stiles suggests Derek. Allison points out that if Scott can catch an arrow then Derek definitely can. Stiles just tells her to shoot one of the other three, and Allison corrects him that there are two. Isaac is missing. Isaac comes up the hallway behind them and throws both Stiles and Allison to the floor.
Lydia and Jackson hear crashing downstairs. Lydia goes to investigate, but Jackson falls to his knees and grabs the back of his neck in pain. Allison appears and tells Lydia to get back in Scott's room because someone is trying to break in. Lydia does and notices that Jackson is missing and the window is open. She calls the cops.
Allison goes into Scott's room and sees kanima venom on the window. She calls for Stiles and tells him that it's there. Erica breaks into Scott's room, and Allison has her crossbow aimed at her heart. Erica taunts her, saying that she thinks Scott will be an easy boyfriend to steal. Allison shoots a bolt, and Erica catches it. Allison had covered the bolt in kanima venom, so Erica goes down. Allison kneels down next to her and brushes her hair back. "I thought you were psychic. Bitch."
Outside, Derek and Boyd watch the house to see how their plan is progressing. Lights go out and there's roaring. Then the front door opens and Isaac and Erica fly out. Scott, Allison, and Stiles step out onto the porch. "I think I'm finally getting why you keep refusing me, Scott. You're not an omega. You're already an alpha of your own pack. But you know you can't beat me." Scott tells him that he can hold him off until the cops arrive. The kanima crawls on the roof and roars at them all. Derek tells Boyd to get Isaac and Erica out of there. Then Lydia rushes out of the front door. "Would someone please tell me what the hell is going on!" And they all realize that it's Jackson. The kanima crawls up next to a car and puts its hand on the window. The driver puts his hand up to match it. And then the kanima runs away.