Scott reveals to Allison that her mother tried to kill him, while Derek discovers Erica's body. Derek, Isaac, and Scott seek help from Chris 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 discover Jennifer is inside; Derek saves her. Stiles discovers 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 to offer as human sacrifices, just as Sheriff Stilinski discovers a third dead girl, killed the same way.