A powerful new Alpha, one of the hales, was building a pack. And anyone who has ever looked up human sacrifice before knows that the druids had a pretty big hard-on when it came to giving one up to the gods. And you know who else is a virgin? Deaton: Lydia? Derek: Get out. Deucalion: No. Deucalion: Now you see the one problem with being in an Alpha pack. Isaac: Derek, please. Isaac: Oh, Mr. Harris? Kill my own pack. Left his car, his dog. Scott: Found something. So work on that. Stiles: Because Scott's dealing with the Alpha twins. They weren't serial killers. They... they'll figure this out! You want to kill me? [Dog whimpers]
Kyle: Looks like he knows who the Alpha is.
Plan: A: The body; Q: What is found of the latest murder victim? A: The Alphas attack Derek; Q: What happens when the body of the newest victim is found? A: Deucalion; Q: Who wants Derek to kill his pack? A: his own Betas; Q: What does Deucalion want Derek to kill to join the Alpha pack? A: their power; Q: What does Deucalion want Derek to absorb from his Betas? A: Lydia; Q: Who is the other person who figured out that the serial killer was a Darach? A: a dark or evil druid; Q: What is a Darach? A: the killer; Q: Who did Mr. Harris seem to know? A: Isaac; Q: Who moves in with Scott? A: Scott; Q: Who does Isaac move in with after Derek kicks him out? Summary: The body of the newest murder victim is found. The Alphas attack Derek, and Deucalion offers him a proposition: join the Alpha pack by killing his own Betas and absorbing their power. Stiles, Lydia and Deaton figure out that the serial killer is a Darach, a dark or evil druid . Mr. Harris is murdered next, though he seemed to know the killer. Derek, aware that Deucalion wants him to kill his pack, kicks Isaac out, so Isaac moves in with Scott.