Dexter is threatened by another serial killer who knows his dark secret and who is nicknamed the "Ice Truck Killer". At the same time, Dexter's sister, Debra, is transferred to the Homicide Department.
The serial killer continues to threaten Dexter, making him feel anxious and stressed.
Dexter and his sister Debra try to convince their boss not to go after a security guard they think has been mistakenly identified as the Ice Truck Killer.
The serial killer begins a diabolical plan to leave parts of his victims' bodies in locations linked to Dexter's memories from his childhood, compelling him to face his distant, troubled past.
The Homicide Department is shaken when the Ice Truck Killer's most recent victim is found mutilated but not dead, while Dexter finds himself in trouble when he begins pursuing some killer.
The serial killer leaves Dexter an unpleasant surprise at the site of one of the latter's latest murders, putting him in the crosshairs of his co-workers in the Homicide Department and damaging his career.
The serial killer is identified at last, but something about the suspect worries Dexter, who also has to deal with the return of Rita's paroled former spouse.
A woman's apparent suicide leads Dexter to suspect her psychiatrist, but he is surprised when he pays a visit to the suspect that causes dark secrets from Dexter's troubled past to be revealed.
Dexter goes away for the weekend but discovers that his biological father, whom he thought had been dead for thirty years, has recently died, leaving him everything he owned, including his home.
The serial killer commits a shocking crime, forcing Dexter to face a terrible memory from the past, and Rita is forced to hire a lawyer when her ex-husband sues for custody of their kids.
As the serial killer abducts someone close to him, Dexter is forced into a trap that will upend his life forever, while Sergeant James Doakes begins to become suspicious of Dexter's strange behavior.
Dexter follows clues left by the serial killer in an attempt to save his kidnapped relative, while Rita's former husband tries to persuade her that Dexter should stay away from their kids.