Dexter's world is rocked when a rival serial murderer, dubbed the Ice Truck Killer by the media, privately contacts him and reveals that he knows Dexter's grisly secret. Meanwhile, Dexter's sister, Debra, is transferred to Homicide.
The Miami Metro Police Department investigate the murder of an undercover officer, while Dexter stalks another victim. Debra discovers a piece of evidence in the Ice Truck Killer Case that helps her get a promotion.
While LaGuerta focuses the department's attention on a potential suspect in the Ice Truck Killer Case, Debra continues to look elsewhere. Doakes pays a visit to drug lord, Carlos Guerrero. Flashbacks show Dexter killing his first human.
The Ice Truck Killer leaves a clue at the scene where Dexter has dispatched his latest victim, and Dexter is worried that someone might have witnessed his killing. Rita is trying to deal with her ex-husband.
Rita must deal with the return of her menacing, recently paroled husband, Paul Bennett. The Ice Truck Killer is supposedly identified, but Dexter is skeptical.
The strange suicide of a powerful woman leads Dexter to suspect her shrink of murder, but he gets a shock when a visit to the suspect opens up dark secrets from Dexter's past.
While on a weekend getaway with Rita, his sister and her new beau, Dexter learns that his biological father, thought to be dead for 30 years, has just passed away, and that he's willed his son everything he owned.
Dexter Morgan is sent to investigate a blood-soaked crime scene, and is gripped by a suppressed memory. Meanwhile, Rita is charged with assaulting Paul and could lose the children in a custody battle. Angel investigates a hunch regarding The Ice Truck Killer.
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.
