When Dexter attends his 20th year high school reunion, he finds a potential victim. LaGuerta and Batista get divorced, and LaGueta gets promoted while Batista is temporarily made lieutenant. Quinn proposes to Debra, but she is not yet ready. Dexter is suspicious about an ex-con minister who helps other ex-convicts. However, it turn out that his suspicions are wrong. A prostitute murder intrigues and reminds Dexter of a serial killer from the 1980s.

Two religious murderers kidnap a runner and force him to repent for his sins. They also organize a crime scene that recalls the book of Revelation using pieces of the Runner’s corpse tied together with mannequins. Meanwhile, Harrison needs to have surgery, which makes Dexter to rethink his views about faith. While examining the angel’s wings from a Doomsday killing, Dexter finds that unique glue was used to attach the wing, and he identifies Travis with this information. He then decides to kill Travis, only to realize that Travis is just Gellar’s tool. Masuka also hires Louis Green to help him with the ice truck killer case missing evidence.

Brother Sam is shot in his shop by an unidentified person and is rushed to hospital. He eventually passes away, having told Dexter to forgive Nick. Dexter decides to kill Nick but later changes his mind and asks Nick to turn himself in. When Nick refuses to turn himself in, Dexter drowns him with Brian watching. Brian stays with Dexter as he disposes of the body.

Dexter continues to pursue the Doomsday Killers, all the while staying ahead of the Homicide Division. Upon finding the frozen corpse of Professor Gellar, Dexter realizes that Travis is the killer and that he is actually his dark passenger. Debra realizes how much she relies on her brother.