In the aftermath of the death of the Ice Truck Killer, Debra makes an uneasy return to work and Dexter finds that he's “off [his] game and distracted” and unable to kill; divers make a gruesome discovery; Rita's ex asks for her help in getting out of jail.
Little Chino strikes again, so Dexter works up another plan to nail him; the FBI sends a special agent (Keith Carradine) to work on the “Bay Harbor Butcher” case; and Debra freaks out on the job. Also, Rita confronts Dexter about his erratic and suspicious behavior.
Dexter deals with a smooth-talking, despicable used-car salesman who's dying to do business with him; Rita suspects Dexter has a drug problem and insists that he get into a program, which throws him into the path of a mysterious and attractive woman (Jaime Murray).
Rita's estranged mother (JoBeth Williams) visits and senses something is wrong with Dexter; Masuka thinks he's developed a lead in the Bay Harbor Butcher case, which has Dexter concerned; Doakes heads a murder investigation involving a military special-ops ranger; Dexter's sponsor (Jaime Murray) has some unconventional ideas about helping him; Angel's interrogation of a witness crosses a line.
In an attempt to shake the task force off his trail, Dexter sends a manifesto to the newspaper detailing previously unreleased information and he also sets up Doakes in an effort to get him off his case. Also, Deb's relationship with Special Agent Lundy (Keith Carradine) takes a surprising turn; and Rita confronts her intrusive mother (JoBeth Williams).
Special Agent Lundy (Keith Carradine) decides to take the investigation “where the chase leads [them],” pointing in the direction of the police force; a nosy neighbor (Bruce Weitz) supplies Deb and Batista with a lead in the case; Dexter is attacked by an assailant he recognizes as the “rededicated serial killer” who murdered his mother.
The ever-persistent Doakes tracks down Dexter to the scene of his latest killing, where he devastates Dexter with a surprising revelation about Harry; Lundy's task force zeroes in on the Bay Harbor Butcher.
Dexter dodges bullets both figurative and real as he is forced to decide the fates of those he cares about most; Lila attempts to blackmail Dexter and makes a startling discovery that changes the nature of their relationship.
Special Agent Lundy (Keith Carradine) and the task force believe they've solved the case of the Bay Harbor Butcher, but Dexter might not yet be out of the woods as Lila discovers his "enormous secret" and tries to use it against him.