As Dexter stalks his next victim, a drunk driver who is about to be acquitted for vehicular homicide that resulted in the death of a teenage boy, the Ice Truck Killer strikes again and later gets in touch with Dexter. Meanwhile, when a cop is found murdered, Dexter helps Doakes and Debra investigate a crime boss who they believe is responsible.

Dexter is finding it hard to have closure on killing his brother. There is a new FBI agent to head the "Bay Harbor Butcher" case. Debra is finding it tough to put the past behind her.

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.

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.