TEXT: [PREVIOUSLY_ON] Heather: You know what I want for my birthday? To not be a 17-year-old virgin. Aah! Sheriff: All her friends say you're the last person who saw her. Derek: Wanna help? Find something real. Scott: Okay. They're on our side now. Derek: Then maybe you should tell her what her mother was actually trying to do that night. Stiles: There's a dead body. It's Erica. Scott: Who's the other girl... the one locked in there with Boyd? Derek: She's my sister... my younger sister! Stiles: Scott, you gotta get out of there. They haven't felt the full moon in months. Derek: No, don't break the seal! Lydia: Aah! Billy: A! Got one! Breanne : What are you doing, dumbass? You're supposed to put holes in the lid. Otherwise you'll kill them. Billy: Do I have to let him go? Breanne : Do you want him to die? Billy? Run! Run! Billy: He's gonna get in. He's gonna get inside. Breanne : Shut up, shut up. Derek: You lost them? Scott: Yeah, I kind of had to. Derek: Wasn't exactly the plan. Scott: I know, which is why I think that we should stick together. Trust me, he's too strong, too fast, and way too angry for one person to handle. We've got to do this together. Derek: Look, I'm at the trails by the entrance to the preserve. Can you meet me here? Scott: Yeah. Just got to drop something off first. Lydia: Mom, I'm going to the store. Mom, do you hear me? Of course you didn't. You would have heard me screaming like a lunatic. Lunatic. Scott: Is it them? Derek: We're not the only ones that decided to stick together. Scott: Is that gonna make it easier or harder to catch them? Derek: I don't know. Scott: Derek... I saw Boyd try to rip two little kids apart. Are they gonna do that to everyone
SUMMARY:
Scott reveals to Allison that her mother tried to kill him. Derek discovers Erica's body. Derek, Isaac, and Scott seek Argent's help to capture Boyd and Cora before they kill someone. Lydia finds a dead boy and calls Stiles for help. The guys trap Boyd and Cora in the high school's boiler room but realize a teacher, Jennifer, is inside; Derek saves her. Stiles comes face to face with Heather's body in the morgue, killed the same way the boy was. As the two were both virgins, Stiles concludes that someone is murdering them as sacrifices, just as Sheriff Stilinski discovers a third dead girl, killed the same way.