A serial murderer dubbed The Ice Truck Killer leaves clues for Dexter---in Dexter's house; the unit investigates the death of an undercover cop; Deb's excellent police work gets her a transfer to homicide; Dexter sets his sights on avenging the hit-and-run death of a teen whose killer walked.
The Ice Truck Killer strikes again and new homicide officer Debra is assigned the case, but she gets reprimanded for violating the chain of command; flashbacks offer insight into Dexter's homicidal tendencies and take him back to his first time "taking out the garbage"; Doakes gets on the bad side of a drug kingpin.
Dexter learns that his biological father, thought to be dead for 30 years, has just passed away, and that Dexter has been named executor; Doakes has a brush with Internal Affairs when there's a question about his shooting of an armed Haitian immigrant. Elsewhere, Rita's ex pays her an unannounced drunken visit.
While Dexter searches for clues to his past, the Ice Truck Killer strikes again, leaving a dismembered body at a Christmas display; LaGuerta has a run-in with Capt. Matthews; Dexter finds a clue to who stabbed Batista; Deb and Rudy's relationship may be heading to a new level of commitment.