Dexter, a forensic blood spatter analyst, lives a double life as a serial killer who targets other murderers. This season, Dexter grapples with the devastating murder of his wife, Rita, by the Trinity Killer. Overwhelmed by grief and guilt, Dexter abandons his children, Astor and Cody, and commits his first kill outside his code, bludgeoning a man to death in a rage. He eventually returns for Rita's funeral and decides to care for his infant son, Harrison, by hiring a nanny.

Dexter discovers Lumen Pierce, a traumatized woman who witnessed him kill Boyd Fowler, a serial killer. Lumen reveals she was part of a group of women abused by Jordan Chase and his associates. Dexter and Lumen form an alliance, hunting down and killing Chase's accomplices, including Cole Harmon. A major turning point occurs when Dexter is forced to kill his own captive to cover for Lumen. The season culminates with Dexter and Lumen confronting Jordan Chase. After Dexter incapacitates Chase, Lumen kills her tormentor. Lumen then leaves Miami, her vengeance complete, leaving Dexter to face his dark path alone.

Season 5 of Dexter covers episodes 1-12. Here's everything that happened:

Season 5, Episode 1: My Bad - In the immediate aftermath of Rita's murder, Dexter grapples with overwhelming guilt and grief, leading him to abandon his family. He commits his first kill outside of his code, bludgeoning a man to death in a gas station bathroom in a fit of rage. This act, witnessed by the spirit of his father, Harry, allows Dexter to finally express his emotions and realize he loved Rita. He returns for her funeral, delivering a heartfelt eulogy, before deciding to disappear himself. Rita's death at the hands of the Trinity Killer marks a devastating turning point for Dexter.

Season 5, Episode 2: Hello, Bandit - Dexter, struggling to parent Astor and Cody after Rita's death, discovers blood in a rented van, leading him to sanitation worker Boyd Fowler. Quinn's investigation into Rita's murder intensifies as he notices similarities between Kyle Butler and Dexter. Dexter finds multiple bodies in barrels in a marsh, confirming Boyd as a serial killer. Ultimately, Dexter kills Boyd Fowler, but not before Astor and Cody are sent to live with their grandparents.

Season 5, Episode 3: Practically Perfect - Dexter struggles to adapt after Rita's death, hiring a nanny, Sonya, for Harrison. He targets Boyd Fowler, posing as a sanitation worker. After a botched attempt at a kill room and a tranquilizer dart exchange, Dexter finally kills Boyd Fowler in his home. The episode concludes with Dexter discovering Lumen Pierce, a captive woman who witnessed his kill, setting the stage for their complex relationship.

Season 5, Episode 4: Beauty and the Beast - Dexter finds himself in the morally challenging position of saving a life rather than taking one when he encounters Lumen Pierce, a traumatized witness to his kill of Boyd Fowler. After initially attempting to keep her contained, Dexter gains her trust by revealing the fate of Fowler's other victims. Lumen then confesses that Fowler was not her only abuser, hinting at a larger network of tormentors. The episode concludes with Dexter and Lumen forming a tentative alliance, united by their shared trauma and a desire for vengeance.

Season 5, Episode 5: First Blood - Dexter worries Harrison may have a dark side after he scratches another child. Lumen, seeking revenge for her assault, targets Robert Brunner, but Dexter intervenes, revealing Brunner is not one of her attackers. Lumen, horrified by her near-mistake, agrees to leave Miami, but ultimately remains. Quinn hires Stan Liddy to investigate Dexter.

Season 5, Episode 6: Everything Is Illumenated - Dexter is distracted from hunting a new target when Lumen calls for help after shooting one of her rapists. Dexter arrives at the warehouse to find the man alive and attempts to track him. After the man implicates himself by phone, Dexter strangles him to death. Dexter then stages the scene to cover for Lumen, killing his own previously captured victim to make it appear as if he was responsible for the death.

Season 5, Episode 7: Circle Us - Dexter and Lumen identify Cole Harmon as one of Lumen's captors. Dexter frames Boyd Fowler for the murders to divert the police, leading to Cole Harmon's death at the hands of Dexter and Lumen. Meanwhile, a botched nightclub sting operation results in the deaths of an informant and a suspect. The episode concludes with Dexter introducing Lumen to his son, Harrison, signifying a deepening of their complex partnership.

Season 5, Episode 8: Take It! - Dexter attends a Jordan Chase seminar, where he targets Cole Harmon. Lumen is pursued by Harmon, but Dexter intervenes, and they kill him together. Jordan Chase is revealed to be one of Lumen's captors. Meanwhile, Debra faces repercussions for the Santa Muerte case fallout, leading to her suspension.

Season 5, Episode 9: Teenage Wasteland - Dexter and Lumen are interrupted by the unexpected arrival of Dexter's stepdaughter, Astor, and her friend Olivia. Dexter discovers Olivia is being abused by her stepfather, Elliott, leading him to brutally assault Elliott and force him to leave town. Meanwhile, Debra uncovers new evidence in the Barrel Girls case, and Jordan Chase taunts Lumen over the phone, revealing he knows her identity.

Season 5, Episode 10: In the Beginning - Dexter and Lumen identify Alex Tilden as the final captor. Lumen, seeking vengeance, kills Tilden in a brutal act, marking her first kill. Meanwhile, Stan Liddy's surveillance closes in on Dexter's secret. The episode concludes with Dexter and Lumen sharing an intimate moment, signifying a deepening bond as they face their shared darkness.

Season 5, Episode 11: Hop a Freighter - Dexter and Lumen attempt to kill Jordan Chase, but are thwarted by surveillance. Liddy captures Dexter, intending to force a confession, but Dexter overpowers and kills him. Meanwhile, Jordan beats Emily to death to silence her. Dexter finds Emily's body and a blood trail, but Lumen and Jordan are gone, leaving him to question if his pursuit of justice will always end in bloodshed.

Season 5, Episode 12: The Big One - Dexter races to save Lumen from Jordan Chase, only to find himself trapped. After Dexter incapacitates Jordan, Lumen kills her tormentor. Debra arrives at the scene but allows Dexter and Lumen to escape. Lumen departs, her quest for vengeance complete, leaving Dexter alone once more.