Things are really beginning to heat up for Dexter: Doakes' suspicions about him are growing, his victims are escaping, and his body dump site has been found. Meanwhile Paul is troubling Rita over the missing shoe and Debra is going through trauma over the Ice Truck killer incident.

Dexter sets his sights on a new victim: a murderer so repulsive it seems only fitting that he's a used-car salesman. Dexter's been unable to lie to Rita about his midnight activities, which has her thinking that he's a drug addict. She's threatened to leave him if he doesn't commit to a 12-step program to deal with his supposed addiction. While in this recovery, though, Dexter meets a sexy, mysterious woman named Lila.

Dexter is attacked by the man who murdered his mother. Meanwhile, Lila wants to get closer to Dex, and Debra and Lundy close in on the Bay Harbor Butcher.

Dexter realizes it won't be easy to end things completely with Lila. Dexter tries to stay ahead of the investigations as the manhunt for the Bay Harbor Butcher intensifies. An enemy of Dexter figures out his secret.

Recent events spur Dexter into his own investigation of the Trinity killer. His motivations are now personal, and the clock is ticking. But the closer Dexter gets, the more he realizes that Trinity is unlike any monster he’s previously encountered. Meanwhile, Debra blames herself for events that were out of her control, and in so doing pushes away those closest to her. As LaGuerta and Batista close in on the Vacation Murderers, Batista realizes he can use Quinn’s relationship with a certain reporter to his advantage. And when Rita discovers a secret Dexter’s been keeping from her, she begins to realize just how little she knows about the man she married.

Dexter has always known his father’s Code was meant to protect him from exposure. But after committing a serious mistake, he wonders if it could have been designed to protect him from something even more dangerous – human emotion. When he discovers that Trinity is planning an out-of-town trip, Dexter sees an opportunity to ride along and gain insight into the mind of a fellow monster.

Dexter must make a choice; Quinn stirs up trouble for Dexter but supports Deb.

Dexter's situation grows desperate when he discovers that Lumen's been set up. Despite knowing he's being baited into a trap, Dexter risks everything to make sure he doesn't fall into the same mistake again. In the Barrel Girls case, Debra lets her personal feelings lead her instincts once she concludes that vigilantes are more than just a theory. Quinn finds himself in a troublesome situation, which only Dexter can help him out of.