After witnessing her brother kill, Debra attempts to reconcile with Dexter while struggling to cover up their involvement with the murder. Meanwhile, Detective Mike Anderson has an unfortunate run-in, Quinn and Batista begin to make amends, and LaGuerta finds evidence that causes her to re-think the closed Bay Harbor Butcher case.
When a local convict claims he has new information regarding a 15-year-old crime spree, Miami Metro sets out to unearth new evidence on the case. Debra attempts to cure Dexter of his killer tendencies. Meanwhile, the Mike Anderson case leads to the Ukrainian mob and a vengeful Louis won't stop meddling with Dexter's life.
Dexter tries to bring Debra on board with his new target. While the Ukrainian mob seeks revenge for the killing of one of their own, Quinn grows close to a dancer at their strip club. LaGuerta, convinced the Bay Harbor Butcher is still out there, attempts to enlist Batista to help her re-open the case.
After capturing a deadly killer, things go awry for Miami Metro, sending Debra into a tailspin. In an effort to help his sister, Dexter enters into a dangerous game of cat and mouse, while the Ukrainian mob continues to seek revenge.
While trying to uncover why Louis was killed on his boat, Dexter must out-maneuver Isaak, who's after Dexter - and Debra. New leads are brought to light on the Wayne Randall killing spree case by his alluring former accomplice, Hannah McKay, who Dexter discovers has a secret.
Debra gets to know a local crime writer who's dug up some incriminating dirt on Hannah McKay - Dexter's newest obsession. Quinn gets an offer he tries to refuse and Batista is drawn to a new business opportunity. LaGuerta keeps digging into The Bay Harbor Butcher case.
Things heat up as Dexter and Hannah grow closer, and when Sal Price discovers the two are involved, he wants the exclusive story. Sal helps Debra uncover new evidence about Hannah, while Quinn makes questionable choices to protect his girlfriend, Nadia.
Dexter tries to keep Debra in the dark about his relationship with Hannah, but a surprise visit from a few people from his past throws a wrench into Dexter's plans. Now out of jail, Isaak renews his pursuit of Dexter, while Quinn continues his power struggle with the Koshkas.
Dexter is preoccupied with Isaak still on the loose, but an internal struggle within the Koshka Brotherhood could work to Dexter's advantage. And while Miami Metro is on the hunt for a Phantom Arsonist, Dexter goes to great lengths to protect his relationship with Hannah, asking a favor of Debra that causes her to question her loyalty to Dexter.
A surprise visit from Hannah's father puts Dexter on alert and the Phantom Arsonist's crimes become more gruesome. Defending Nadia's honor forces Quinn into a dangerous situation and LaGuerta brings in Matthews to help her with The Bay Harbor Butcher case.
As Christmas approaches, Dexter tries to balance his life with Hannah and his relationship with Debra, but unbeknownst to Dexter, Debra follows up on a potentially incriminating tip. Dexter learns that the man responsible for ordering his mother's death has been released from prison, and zeros in for a kill that might end all kills.
As LaGuerta closes in on Dexter's secret, Dexter struggles to protect himself, Debra and the life he's built.
