Lydia is in bad shape. Parrish finds her by the nemeton, and she's hypothermic and non-responsive. She had carved a Sheriff's badge into the nemeton. Lydia's mom sends Lydia to Eichen in order to keep her safe. Little does she know, in the present (everything else is flashbacks, remember?) a doctor at Eichen House is drilling into Lydia's head and asking her about Theo.
She uncovers that Theo killed his sister for her heart, and then the Dread Doctors performed a heart transplant on 10 year old Theo. Lydia states that the Dread Doctors have made a perfect killer. Then, Theo and his chimeras come to break out Lydia, but Theo's only doing that in order to catch himself a hellhound.
The Sheriff isn't doing too well. He survived surgery, but then something goes wrong. Stiles thinks he's been poisoned, and so he reaches out to Theo in the hopes that he might know something. Stiles lies to Theo and tells him that Liam killed Scott, meanwhile Scott is upstairs listening to Theo's heartbeat. After the chat with Theo, Stiles and Scott work on locating a missing chimera who might have been the one who attacked the Sheriff.
Liam feels guilty that he almost killed Scott and that he wasn't there for Hayden when she was dying. When he finds Hayden's scent, he drags Mason along on a search that leads them to the Nemeton and a very alive Hayden.