This week's episode of "Teen Wolf" begins with a flashback to the night Matt found out Jackson was the Kanima. By watching a live stream of the camera he let Jackson borrow on his smart phone (kids these days and their crazy technology) he sees him change. Then they share a moment of matching up their hands together in recognition, like Tarzan and Jane only scalier. They also share a vision of the Kanima killing the Mr. Lahey, and it seems to dawn on Matt that that murder was for him. And so they become a pair, a boy and his supernatural murderous dog.
Scott and Stiles convince Stiles' dad to go to the police station to re-examine the evidence until it all points to Matt. They find footage of Matt in the hospital the night the pregnant girl, the one victim who wasn't killed by the Kanima, was murdered. When they see footage of him taking to Scott's mom he calls her up and asks her to come in and make a statement about seeing him there that night. And then, just as all the pieces are starting to come together, Matt shows up with a gun, killing the officer at the front desk. On the plus side, that makes him look really guilty.
Dr. Deaton shows up at the Hale house to revive Derek and explain he helps him because he promised Derek's mother he would. He also urges him to find Scott and Stiles (and learn to trust Scott).
Alison, still devastated from her mother's death, is incredibly emotionally manipulated by her grandpa into a murderous rage directed at Derek. She proceeds to go full warrior, throwing out all her girly teenage accessories away and changing into dark colored warrior clothes, which seems unnecessary; even Buffy wore lip gloss.
Back at the station Matt has Scott and Stiles destroy all the evidence that points to him. They think he might let them go when Derek shows up, only to be rendered paralyzed by the Kanima. Stiles is paralyzed next, and Matt reveals he knows Derek and Scott are werewolves. When Scott's mom shows up Matt honors his promise not to hurt her but shots Scott instead. As his mom becomes more and more frantic about the wound Matt realizes she has no idea her son is a werewolf and that the injury will heal itself. Matt then reveals what he's really there for- the Beastiary. He needs it to figure out why his skin is morphing into Kanima skin. Because of the desperation of the situation no one thinks to make a proper moisturizer joke.
At Allison's house she gets a text that reveals the fact that Derek is at the police station, and leads her father and grandfather there with the sole purpose of killing Derek and any werewolf that gets in their way.
Finally with Scott and Matt alone in one of the station's rooms, the back story behind his rage comes out. When Matt was younger he went over Issac's house to hang out and walked into the swim team's drunken victory party. Issac's brother tossed him into the pool not knowing he could swim, and they were all too drunk or disinterested to notice he was drowning. Mr. Lahey saved him, but afraid he'd get in trouble for giving the teens alcohol, he bullied him into keeping his mouth shut. Matt described how the memory of nearly dying under water haunted him, as did knowing so many people had stood by and done nothing to help him. He then explained he accidentally took a picture of Lahey at Kate's funeral and all his anger came back. The next day Lahey was dead. After the creepy hand moment with the Kanima he realized if he snapped a picture of any of the other swim team kids who didn't save him they'd die too, so he got to work on his plan of vengeance.
And just when they're having a moment, Allison and company show up with machine guns blasting, because that's how they roll. When Allison bumps into Scott in the hallway she demands to know where Derek is, and when he doesn't tell her she kind of implies she isn't above killing him too. Allison then learns like guns on zombies arrows are not effective on Kanimas. She's attacked and paralyzed, but her dad is able to carry her to safety.
In the holding area where Matt had Stiles' dad chained up and Scott's mom behind bars the Kanima, Matt, and Derek in full wolf mode show up to battle it out. When Scott shows up, also all wolfy to help, his mom catches sight of his face and backs away slowly, completely terrified. Scott looks hurt that his mom seems to reject him as a werewolf, but I think it's only fair to give her a little time and explanation before dubbing her prejudice against the supernatural. To make Scott's problem's worse Derek overhears him talking to Allison's gramps and reveals he's been giving him information. So much for Derek learning to trust people.
Gramps drags Matt down to the river, drowns him, and all too willingly becomes the Kanima's master instead of killing it like everyone he knows thought he surely would. His Kanima bonding moment is witnessed only by Peter, who'll probably figure out a way to use this little tidbit of information to his advantage.