In a flashback, we see the exchange between Jackson and Matt where Matt loans him his camera. Only this time, we see Matt go to his car and call up a Ustream app on his phone. It connects to the camera he just gave Jackson. As Jackson falls asleep, Matt sits back and watches. He starts to fall asleep himself but wakes up in time to see Jackson sit up with glowing eyes. He watches Jackson's transformation into the kanima and then hears something approaching his car. In his sideview mirror, he sees the kanima coming around the car. The kanima starts to lift its hand, and Matt places his hand on the window to match it. They share the memory of Mr. Lahey's murder, which means that Jackson has already previously transformed.
Sheriff Stilinski, Stiles, and Scott meet to talk about Scott's discovery that Matt is the kanima's master. The Sheriff doesn't believe that Matt's the killer. Stiles argues that everyone knows how the police attempt to track down murderers, so all Matt had to do was track down which class all his victims had in common. His dad points out that Kara wasn't in Harris's class, which they both already knew. Scott confirms that they know it's Matt without being able to say why. Stiles says that Matt stole Harris's car and purposefully left evidence to set him up. The Sheriff asks them for motive. "Isn't it obvious! Our swim team sucks! They haven't won in like six years. Okay, we don't have a motive yet." But then neither does Harris. The Sheriff asks the boys what they'd like him to do. Scott says they need to look at the evidence, and the Sheriff tells him that it's in the station where he no longer works. "Trust me, they'll let you in," Stiles tells him. His dad is incredulous that he would suggest he is trustworthy, so Stiles points over his shoulder. "Trust Scott?" The Sheriff agrees to trust Scott.
They head to the sheriff station at 2am. Stiles tells Scott that they need to start by looking at the hospital murder, which is the only one not committed by the kanima. An officer lets the Sheriff into the office. They start looking through the hospital security camera footage. Scott thinks he sees something and asks the Sheriff to scroll back. Stiles recognizes the back of Matt's head because he sits behind him in history. "Look at his jacket. How many people do you know who wear black leather jackets?" "Millions. Literally." Scott asks him to scroll forward, and they see Matt talking to Melissa McCall. Scott calls him mom, and they ask her if she remembers Matt. She tells him that she talks to a lot of people, so they send her Matt's yearbook photo. She says that she remembers Matt because he was tracking mud in the hall. The Sheriff pulls out a file. They have footprints from the trailer site, and if they match that puts Matt at the trailer, the hospital, and the rave. The Sheriff corrects him. There's a credit card receipt for an oil change signed by Matt at the Armor Tire a couple of hours before Stiles arrived. The Sheriff says that four is enough for a warrant. He has Scott call his mom back and ask her to come to the station. Stiles heads out to the front desk to tell them to let Melissa in when she arrives, but there's no one there. He finds the woman at the desk dead on the floor. Her gun is missing. Stiles turns around, and Matt has the gun pointed at his face.
Derek is in a white place. Someone calls his name, but it's fuzzy. "We don't have much time," the voice says. There's a piercing sound, and then Derek blinks awake. Dr. Deaton is kneeling over him. Derek asks what the sound was, and Deaton holds up a dog whistle, grinning. Derek smirks and tries to stand, but he stumbles. Deaton catches him and tells him that he's going to be weak for a few hours. Derek flashes back to Peter coming back to life and realizes it wasn't a dream. Deaton tells him that he's still an alpha, "but, as usual, not a particularly competent one." Derek lets the insult go and asks where Peter is. Deaton doesn't know. Derek demands to know why Deaton is helping him. "Helping your family actually used to be a pretty important part of my life. Helping you was a promise I made to your mother." Derek backs off and says that Laura told him there was a sort of advisor to their family. Deaton says that Peter's resurrection comes with a price. He will be physically weak, so he will rely on his intelligence and cunning. "He's going to come at you, Derek. He'll try to twist his way inside your head, preying on your insecurities. He'll tell you he's the only way you can stop Gerard. Do not trust him." Derek replies that he doesn't trust anyone. Deaton replies that if he did he might be the alpha he likes to think he is. "Unfortunately, the one person you should trust doesn't trust you at all." "Scott." Deaton tells him to find Scott as fast as he can because Gerard always has a plan and it's so far going exactly how he wants. Derek spends most of the conversation looking worried, even while Deaton is insulting him.
Scott says that his mom is on her way, and then the Sheriff sees Matt leading Stiles back in at gun point. The Sheriff tells Matt that there's a solution here that doesn't involve a gun, and Matt replies that he's more correct than he knows. The Sheriff tries telling him that he doesn't want to hurt people, but Matt actually does. The three of them weren't on his list, but he can add them if Scott keeps doing things like trying to dial his cell phone in his pocket. Matt makes them all put their phones on the desk. Then he has Stiles cuff the Sheriff onto one of the benches by the cells. Matt leads Scott and Stiles away, and as they pass a hallway, they see all the other officers the kanima has murdered.
Allison sits at home on her bed. Gerard tries to talk to her, but she tells him to leave. He says that he just wanted to give her something from her mother but that it can wait. It's enough enticement to get her to ask what it is. Victoria wrote a suicide note that could be given to the police. She wrote a separate note to explain the truth to Allison. Gerard gives her that note with the instruction that she has to burn it after she reads it. He says that he wasn't close to his mother, but having read what Victoria wrote, it made him wish he had been. "If there words were written for me, I don't know how I could sit still until someone paid for her death. Any pity I'd have for Derek and his pack would be burned out by a white hot desire for retribution." Gerard melodramas a little more, manipulating Allison's grief into rage.
Matt has Stiles and Scott destroy all the evidence that points to him. Stiles asks if they're all good now. Scott's mom pulls up, and Scott begs him not to hurt her. Matt orders the two of them to the front door and has Scott open it. Scott does, and it's Derek. "Oh thank God." But then Jackson tosses the already paralyzed Derek onto the floor.
Allison burns the letter. She looks around her desk at all her old things and starts throwing them out. She gets rid of all her girly things and then goes into her closet looking for black clothes. She starts gearing up for battle.
Scott stares down at Derek while Matt leans over him. "This is the one controlling him? This kid?" Derek asks. "Well Derek, not everyone's lucky enough to be a big bad Werewolf," Matt replies. Matt has learned about Werewolf, hunters, and kanimas. It's like Halloween every full moon. "Except for you Stiles. What do you turn into?" "Adominable Snowman, but it's more of like a winter time thing. You know, seasonal." Matt has Jackson paralyze Stiles, and Stiles falls on top of Derek. Derek grumbles for someone to get Stiles off of him, but Matt thinks they make a good pair. He taunts Derek about how strange it must be for him to feel so helpless. "Still got some teeth. Why don't get down here a little, huh, we'll see how helpless I am," Derek says. "Yeah, bitch," Stiles adds. Another car pulls up, and Matt tells Scott that if he does what he says neither he nor Jackson will hurt Melissa. Stiles yells at Scott not to trust him, and Matt rolls him off Derek so he can put his foot to Stiles's throat. Scott promises to do what he wants if he'll stop choking Stiles. Matt orders Jackson to move Stiles and Derek. Melissa comes in to find Matt holding a gun on Scott. Scott tells his mom to do what Matt says because he promised he wouldn't hurt her. Matt confirms and then shoot Scott. Melissa screams, and the Sheriff stands up, shouting their names. Matt orders Melissa back, and Scott begs her to comply. Matt locks Melissa in a cell. She thinks Scott is going to bleed to death. Matt tells Scott to go back to the front of the station, and there he demands the bestiary. Scott tells him that Gerard is the one who has it. Matt claims he needs answers. "Answers to what?" Matt lifts up his shirt and shows them his skin, which is turning into the kanima's hide. Stiles and Derek on the floor both look shocked.
Allison holds her phone up to her dad. It's a text message demanding the bestiary. Allison tells him it's not from Scott because Scott wouldn't have texted her and wouldn't have mentioned Derek. Chris thinks that the kanima is probably there along with the one controlling it. They get out floor plans for the sheriff's station. They figure the night shift is all either dead or paralyzed. Gerard thinks this is just what they've been waiting for. Allison asks what they should do, and Gerard tells her that she's the one who makes those decisions now. "Make the decisions from a vantage point of strategy over emotion and we'll follow your lead." Allison declares that she wants Derek dead. Chris asks about Scott, and Allison replies that Scott didn't force Victoria to kill herself. She can prioritize targets, and she's prioritizing Derek. Chris asks about the pack. Allison says that they kill them if they try to protect Derek. Gerard is pleased with her bloodlust.
Stiles asks Derek if he knows what's happening to Matt. Derek replies that the book isn't going to help him. He can't just break the rules like he has been. The universe will balance things out. Because Matt's been using the kanima to kill people who don't deserve it and killing people himself, he's turning into a kanima. "Will he believe us if we tell him that?" Stiles asks. "Not likely." Stiles asks if Matt's going to kill them all when he gets the book. Derek says yes. Stiles asks if they just sit there and wait to die. "Unless I can figure out a way to push the toxin out of my system faster. Like triggering the healing process." Stiles glances down and sees Derek digging his claws into his own leg.
Matt gets Scott alone and says that he's sorry that Scott will have to explain how his bullet wound healed so quickly. But what's even worse is that Scott doesn't even recognize how lucky he is that he gets to heal from something like that. Scott asks Matt if he drowned. Matt explains that Mr. Lahey let the swim team drink. They were all at Isaac's house. Isaac had a first edition Spiderman or Batman comic and they were going to trade. But then Matt saw the party and everyone throwing each other into the pool. Camden grabbed Matt and threw him in. While he was under, he could see Sean and Jessica feeling each other up, as well as Tucker and Kara. While Matt was dying, everyone else was laughing. Suddenly, Matt was by the side of the pool, and Mr. Lahey was telling him to keep quiet about what happened. "This is your fault. You don't know how to swim? What little bastard doesn't know how to swim? You say nothing. You tell no one." Matt kept the secret. He would wake up gasping from breath, and his parents thought he'd developed asthma. Every time he closed his eyes, he was drowning. And he didn't see the white light you're supposed to see when you die. When he was at the Argents' funeral, he took some photos and happened to take one of Mr. Lahey. When Matt saw the photo, he was filled with rage. He wanted to see him dead. And the next day it happened. It was like the Furies coming down to punish Orestes. Scott doesn't know who Orestes is. Matt explains that the Furies were deities of vengeance. They had tears of blood and snakes for hair. If there was a crime that went unpunished, the Furies would do the punishing. When Matt saw Jackson the night that he recorded himself, their bond was cemented. Then he went to Tucker's garage and paid for an oil change. He took a photo of him, and a few hours later he was dead. The timeline is screwy here, because Bennett actually died before Tucker, but the point is that all Matt had to do was take their picture and Jackson would kill them.
Stiles asks Derek if his hypothetical healing is getting any less hypothetical. Derek says he thinks so because he can move his toes. Stiles sighs and tells him that he can move his toes, too. Suddenly, all the lights go out. Matt demands to know what's going on, but Scott doesn't know. The Argents open fire with automatic weapons. Everyone ducks for cover.
Gerard quotes Shakespeare. "Love is the smoke made from the fumes of sighs." And then tosses in smoke bombs. Scott takes the chance to escape. He plows into Jackson and goes straight for Stiles. Derek tells Scott to take Stiles, as he's starting to be able to move. Scott hurries Stiles away and locks a door between him and Jackson, as though that will keep Jackson from following. Chris and Allison come into the station. They hear Sheriff Stilinski shouting as he tries to pull the bar in the holding cell free from the wall. Derek is mobile again and his eyes flash red.
Scott puts Stiles into a chair and tells him not to move. Stiles stares at him sarcastically. Scott goes running back out in the station and runs into Allison. She demands to know where Derek is. "What are you doing?" Scott asks. She tells him to give up Derek or get out of her way. Scott can tells that something's wrong, but he doesn't know what, and she just tells him to stay away.
Chris and Allison look for Derek in the evidence room. The kanima finds them instead and leaps down on Chris. Allison puts a bolt through its head, but it just pulls it out. Allison runs and ditches her crossbow, switching to her knives instead. She hides behind a desk and waits. When it's looking the other way, she leaps over some desks and drives a knife into its chest. The kanima grabs her by the neck, and Allison shoves a dart into its stomach. The kanima paralyzes her and drops her to the floor. Matt kneels next to her and tells her she should have given him a chance. "If I can't have you, no one can!" There's a noise in the distance, and Matt goes to investigate. While he's gone, Chris picks up Allison.
Sheriff Stilinski manages to rip the ring off the wall at last, while Stiles struggles to crawl into the room with them. Matt runs up to the Sheriff and punches him, knocking him out. Melissa begs Matt to let her see Scott, and Matt yells at her for being clueless. Derek appears in one doorway, growling and eyes glowing. The kanima appears in another. Derek and the kanima fight, while Melissa watches. Derek tries to keep the kanima away using a chair, but the kanima throws him hard into a wall. Then it crawls on the bars in front of Melissa. While it's paying attention to her, Scott shoves his claws into its back. Melissa asks Scott if he's okay, and he turns to look at her while he's still wolfed out. She starts to cry and backs away from him. Rather than try to explain, Scott leaves to help Derek with the kanima. He runs into Gerard in the hallway and says that it wasn't supposed to happen like this. He's done everything that Gerard has asked him to do. "I'm part of Derek's pack. I've given you all the information that you wanted. I told you Matt was controlling Jackson." Gerard tells Scott to leave Jackson to them. Gerard drops the pill box that he's been taking pills from all season, and Scott hands it back to him. Derek overhears their conversation and knows he's been betrayed.
Matt runs from the station and to a bridge, where he encounters Gerard. Gerard throws him into the river and drowns him. He leaves Matt's body in the water and finds the kanima sitting under the bridge waiting for him. Peter Hale watches Gerard greet the kanima.