Season 7 picks up with Debra, having caught her brother in the act of murder, taking a stab at covering up their involvement in the crime. Meanwhile, LaGuerta considers reopening the Bay Harbor Butcher case when new evidence resurfaces.
Miami Metro reopens a 15-year-old case based on new evidence provided by a local convict; and Debra works to cure Dexter of his homicidal urges. Meanwhile, the Mike Anderson case appears to have ties to Ukrainian mobsters.
Dexter takes aim at a new target and attempts to get Debra to pitch in; the Ukrainian mob sets out to avenge the killing of a member; and Quinn gets chummy with a dancer at the mob's strip joint. Meanwhile, LaGuerta is convinced the Bay Harbor Butcher is still at large and recruits Batista in her efforts to reopen the case.
Despite apprehending a killer, problems plague Miami Metro and Debra feels the brunt of it. To help his sister, Dexter undertakes a risky game of cat and mouse, and Ukrainian mobsters step up their retaliatory efforts.
Dexter seeks to learn why someone was killed on his boat, while at the same time, he tries to outmaneuver Isaak, who is bent on revenge. Later, the Wayne Randall case takes a positive turn when new leads are brought to light by his fetching former accomplice, whom Dexter learns is harboring a secret.
Debra befriends a local crime writer who claims to have incriminating info on Hannah McKay; Quinn receives a strange offer and he's wont to accept it; Batista contemplates a business opportunity, while LaGuerta hopes to dredge up new evidence in the Bay Harbor Butcher case.
Dexter and Hannah's relationship heats up, which crime-beat writer Sal Price is very interested to learn, so much so that he helps Debra dig up some information on her. Meanwhile, Quinn's attempts to protect his girlfriend lead to some questionable moves.
Dexter attempts to keep his relationship with Hannah a secret from Debra, but that gets blown out of the water when Astor, Cody and Harrison pay him a surprise visit and the news leaks out. Meanwhile, Isaak gets out of jail and steps up his pursuit of Dexter, while Quinn's power struggle with the Koshkas intensifies.
Dexter is unnerved when Hannah's father pays him a surprise visit; the Phantom Arsonist's crimes become more vicious; and Quinn defends Nadia's honor and finds himself in a volatile situation. Meanwhile; LaGuerta asks a former superior for help on the Bay Harbor Butcher case.
It's Christmastime, and Debra learns it may be better to receive when she gets a tip from Hannah's father, one that could lead to incriminating Dexter in a crime. Meanwhile, Dexter discovers that the man behind his mother's death has been released from prison.