Season synopsis
Contains spoilers for this season and earlier seasons.
Dexter and Miami Metro investigate ritual killings staged with imagery from the Book of Revelation. The department attributes the scenes to the Doomsday Killers, Professor James Gellar and his student Travis Marshall, while Dexter follows the clues and struggles with questions about faith as he considers a Catholic preschool for Harrison. He initially suspects Brother Sam, a repentant ex-convict who runs a body shop and helps others rebuild their lives, but instead becomes his friend. After Sam is shot by former employee Nick, Dexter kills Nick when he admits the murder and shows no remorse.
Debra takes over as Miami Metro’s lieutenant after LaGuerta becomes captain, and she and Quinn split when she turns down his marriage proposal. Quinn’s drinking and poor judgment strain his partnership with Batista. Dexter travels to Nebraska after Trinity’s surviving son Jonah reports that his mother and sister are dead; Dexter first suspects Jonah, then learns Jonah killed his mother in anger after his sister’s suicide. Dexter chooses to leave Jonah alive. The DDK investigation leads Dexter to Travis, who insists Gellar is directing him, until Dexter discovers Gellar was killed three years earlier and exists only in Travis’s mind.
Travis marks Dexter as the Beast in his final tableau and nearly kills him, but Dexter survives and returns to Miami. Travis later abducts Harrison to use him as the sacrifice in his planned apocalypse. Dexter rescues his son, knocks Travis unconscious and takes him to the abandoned church where the killings were staged. During the same stretch, Debra attends therapy and recognizes romantic feelings for Dexter. She goes to the church intending to tell him, but sees him plunge a knife into Travis and discovers that her brother is a killer.