Dexter figures out who the Ice Truck Killer is, along with a dark secret from his troubled past. Meanwhile, La Guerta is replaced with a new boss and Angel figures out a way how to track the killer while he's still in hospital.

A copy-cat killer follows the lead of the "Bay Harbor Butcher." Dexter must destroy an incriminating surveillance video.

Lila Tournay finds Sgt. James Doakes imprisoned in an Everglades cabin and learns from him that her object of affection, Dexter Morgan, is the serial killer known as the "Bay Harbor Butcher". She decides to help Dexter and kills Doakes by setting the cabin on fire. Meanwhile, Dexter's sister Debra questions whether her career is more important than her relationship with FBI Special Agent Frank Lundy.

Dexter has put his life back together but things may fall apart soon. His new victim is also being targeted by Assistant District Attorney Miguel Prado. Deb has to decide how to handle Internal Affairs, as they want her to turn on her new partner.

Ramon's career may be in jeopardy due to his obsession with Oscar's killer. Meanwhile, Dexter does a great job in keeping Ramon off balance by manipulation. Deb refuses to "be a rat" after Internal Affairs presses her to come up with more dirt on Quinn. Also, Rita and Dexter decide it's time to tell the children about her "condition," and Angel's quest for companionship nearly get's him in deep water.

It is the day before Dexter's wedding and Dexter must deal with two people targeting him, while preparing for his special occasion. Meanwhile, Angel tells Deb he's put her in for a promotion, but after he finds out some information her shield may be gone before she gets it.

Six months after the season finale, Dexter is now living with three kids and a wife in a new home. Along with his new son Harrison, the complexities of being a suburban father of three is making it difficult for Dexter to concentrate on his work. His lack of sleep leads him to let a murderer walk by bringing the wrong documents to court and causes him to get into a car crash. Now retired Agent Lundy has returned to finally capture the mythical "Trinity Killer" who has arrived in Miami.