Isaac and Derek in “Unfinished Business”

Isaac

Want to figure something out? Because while Scott and Stiles were out there trying to help people from being killed, you were in here, rolling around the sheets with the actual killer! Do you get how many people she's killed? Erica and Boyd are dead, Cora is dying, and you're doing nothing! Why did you do this to us Derek? Was it all about the power? Were you bored? Were you lonely?

Derek

Maybe. [Isaac angrily goes to leave] I told Cora I wouldn't leave. I'll help the others when I figure out how to help her.

Isaac

There's no time! The full moon's coming. The sheriff and Melissa are going to be dead, so I'm going to help them. You can sit here and perfect the art of doing nothing.