Okay I mean Theo is really evil but he’s playing everyone in Scott’s pack really well. This whole season secrets are supposed to tear the pack apart and he’s doing just that. He knows Stiles killed Donovan, Kira talking in her sleep in Japanese and her whole fox spirit and Scott not trusting her anymore. He knows Malia saw the Desert Wolf shoot at her family’s car when it crashed. He could use this against anyone and were seeing it now with Stiles as Theos blackmailing him. For me it seems like Theo is the brains of the Dread Doctors.