Zack abducts Dr. Brennan and tells her not to talk about Booth. When she asks Zack about the nasty scar across his forehead, he mentions that Brennan hasn’t been to see him in some time.

Angela realizes that Zack turned off some of the security cameras when he took Brennan but the cameras covering the outside of the building weren’t tampered with. When Angela realizes that there’s no footage of them leaving, they determine that Zack and Brennan may still be inside the Jeffersonian. 

Booth finds them in the basement where Zack is about to inject himself with truth serum to prove that he didn’t kill anyone. Zack is taken into custody. 

No matter what he says, Hodgins is convinced that Zack is guilty. Zack’s doctor, Dr. Roshan, says he hasn’t been the same since Sweets was murdered. Zack even hurt himself in a fit of rage which gave him the scar on his forehead.

Zack has been hacking Brennan, Hodgins, and Cam’s emails when he’s broken out of the sanitarium, but not Booth’s. Zack says that Booth isn’t his friend. There’s even a wedding photo of Booth and Brennan where Zack tore Booth’s head out of the picture. 

Zack had also set up a dummy account, pretending to be Dr. Alexander Bancroft, the renowned neurosurgeon with whom Hodgins’ doctor has been consulting. He came up with the treatment that gave Hodgins back the feeling in his legs, only it all came from Zack. 

Dr. Karen is back from Kansas City and her behavioral analysis of the killer makes her believe that he has dissociative identity disorder, otherwise known as multiple personality disorder. One personality takes care of the victims while the other brutally murders them. 

Booth and Wendell find a tooth fragment that doesn’t belong to any of the other victims. They head to Graham Reynold’s creepy basement and they find a hidden room with half the remains of another victim, a teenage boy missing the entire lower half of his body. The time of death was ten to twenty years ago. Zack would have been a teenager himself. 

Hodgins goes to visit Zack in custody and thanks him for helping him regain feeling in his legs but Zack tells him the pain doesn’t mean he’ll walk again. The treatment has a less than 1% probability of success but he wanted to give Hodgins hope. 

Dr. Falk has a restraining order against Booth because he hit him when he was looking for Brennan. Falk says the killer has a pathological need for control and will try and get close to Booth and Brennan to manipulate them. 

Dr. Karen wants to let Zack look at the case file. She thinks Zack is guilty and if so, looking at the case file may push his other personality to emerge. Booth agrees but then tells Aubrey to investigate why Karen left Kansas City. Her boss, Paul Crawford says he legally can’t talk about her departure. 

Brennan visits Zack as he goes over the case files. He admits that he’s had lapses in memory. Although Zack doesn’t remember committing the crimes, he and Brennan agree that he is most likely guilty, but Booth says his gut is telling him otherwise. Later Brennan worries Karen may be the killer until she admits that the reason she left Kansas City was that her married boss was hitting on her so she hit him.

Brennan and the team realize that the remains of the fourth victim are actually from a conjoined twin. When Angela reconstructs the face, they realize that it’s Zack’s doctor, Dr. Roshon who has taken Zack back to the sanitarium to put him in maximum security. 

Dr. Roshon tries to drug Zack and kill him. Zack fights back but he can’t kill Roshon when he has the chance. Then Booth arrives and shoots and kills Roshon. 

Hodgins has lost all feeing in his legs, and they fear that this time it might be for good. Hodgins says he’s ready to accept that possibility.

Zack admits that he didn’t kill the lobbyist but he always thought he would have murdered him if told to do so. Now that he realizes that he couldn’t even kill Dr. Roshon to save his own life, he knows his assumption was wrong and asks that the evidence in his original case be reexamined. Booth and Brennan agree.