Dexter Morgan is a blood spatter analyst for Miami Metro who secretly lives a double life as a serial killer, hunting other murderers who have escaped justice. This season, Dexter accidentally kills Oscar Prado, the brother of Assistant District Attorney Miguel Prado. This unexpected event forces Dexter into an uneasy alliance with Miguel, while his girlfriend, Rita, reveals she is pregnant, adding a significant new complication to his life.

As Dexter hunts the drug dealer Freebo, he is discovered by Miguel, who surprisingly thanks Dexter for avenging his brother. Miguel becomes fascinated by Dexter's "dark passenger" and wants to participate in his vigilante justice. Dexter attempts to teach Miguel his code, but Miguel's true nature emerges as he begins to kill outside of Dexter's rules, notably murdering attorney Ellen Wolf. This reveals Miguel's manipulative intentions, turning their alliance into a dangerous game of cat and mouse. Dexter realizes Miguel is a dangerous threat and must be stopped.

The season culminates in Dexter confronting and strangling Miguel Prado to death, framing another killer, George King (known as "The Skinner"), for the murder. Dexter then manages to kill George King after being captured and tortured. The season concludes with Dexter marrying Rita, seemingly embracing a normal life, though a drop of blood on Rita's wedding dress hints at his enduring darkness.

Season 3 of Dexter covers episodes 1-12. Here's everything that happened:

Season 3, Episode 1: Our Father - Dexter mistakenly kills Oscar Prado, the brother of Assistant District Attorney Miguel Prado, while attempting to kill a drug dealer. This unplanned killing leads to Dexter forming an uneasy alliance with Miguel. Meanwhile, Rita reveals to Dexter that she is pregnant, adding a significant new complication to his life.

Season 3, Episode 2: Finding Freebo - Dexter hunts the drug dealer Freebo, who is responsible for Teegan's death. Dexter successfully kills Freebo in a detached garage, but is discovered by Miguel Prado. Dexter claims self-defense, and Miguel, surprisingly, thanks Dexter for avenging his brother's death. The episode concludes with Dexter disposing of Freebo's body in the ocean, while Rita decides to keep their baby.

Season 3, Episode 3: The Lion Sleeps Tonight - Dexter discovers a pedophile, Nathan Marten, photographing Astor. Despite Marten not fitting the usual criteria, Dexter strangles him to death, stating, "Nobody hurts my children." Dexter also grapples with impending fatherhood. The episode concludes with Dexter bringing milk to Rita's house, placing a hand on her belly, and accepting his role as a father.

Season 3, Episode 4: All in the Family - Dexter proposes to Rita, who initially declines but eventually accepts after he uses lines from a disturbed woman he's investigating. Dexter manipulates Miguel's volatile brother, Ramon, into an aggressive confrontation, further isolating Miguel and solidifying Dexter's control. Ramon is framed as unstable and untrustworthy, and Dexter successfully convinces Miguel that he is the only one he can rely on.

Season 3, Episode 5: Turning Biminese - Dexter tracks a husband who murdered two wives for financial gain to Bimini. Meanwhile, Rita experiences a medical emergency during an ultrasound, causing Dexter to re-evaluate his priorities. Miguel Prado's manipulation of Dexter's "dark passenger" escalates as Dexter realizes Miguel's true intentions.

Season 3, Episode 6: Sí Se Puede - Dexter tests Miguel's commitment to his dark path by arranging for them to kill a white supremacist, Clemson Galt. Meanwhile, Debra suspects Ramon Prado is "The Skinner," and Rita considers a new career opportunity. The episode concludes with Dexter successfully killing Galt alone, realizing Miguel is not yet ready to share his kill, and Miguel realizing Dexter has deceived him.

Season 3, Episode 7: Easy as Pie - Dexter is torn between his code and his friendships. He struggles to reconcile Miguel's desire to kill attorney Ellen Wolf with his own rules. Meanwhile, Dexter's terminally ill friend, Camilla, asks him to end her suffering. Dexter ultimately euthanizes Camilla with a poisoned key lime pie, and she dies peacefully, even acknowledging that Dexter was right to kill his brother. Dexter and Miguel reconcile, with Miguel becoming his best man.

Season 3, Episode 8: The Damage a Man Can Do - Dexter reluctantly teaches Miguel Prado the "Code" to kill Billy Fleeter. After Dexter injects Fleeter, Miguel stabs and kills him, finding the act exhilarating. Meanwhile, Debra discovers her informant boyfriend Anton is missing, realizing he's been taken by the Skinner. Dexter proposes to Rita, giving her an engagement ring.

Season 3, Episode 9: About Last Night - Dexter's friendship with Miguel strains as Rita confronts him about suspected infidelity. Debra frantically searches for Anton, who is revealed to be abducted by "The Skinner." Dexter discovers Miguel murdered Ellen Wolf, and a blood test confirms Miguel used cow's blood to deceive Dexter, revealing Miguel has been manipulating him all along. The episode concludes with Dexter realizing Miguel is a dangerous threat.

Season 3, Episode 10: Go Your Own Way - Dexter and Miguel's strained alliance reaches a breaking point as they engage in a dangerous game of cat and mouse. Miguel threatens Debra's career to manipulate Dexter, while Dexter retaliates by exposing Miguel's affair with LaGuerta to his wife, Sylvia. The episode culminates with Dexter being ambushed and abducted as he contemplates his next move against Miguel.

Season 3, Episode 11: I Had a Dream - Dexter is unexpectedly abducted for his bachelor party, only to realize he must now eliminate his best man, Miguel. LaGuerta grows suspicious of Miguel's involvement in Ellen Wolf's murder, leading Dexter to set a trap. Dexter confronts and strangles Miguel Prado to death, framing the Skinner for the murder. Debra learns of her father's affair with a CI, and Dexter asks her to be his best man.

Season 3, Episode 12: Do You Take Dexter Morgan? - Dexter prepares for his wedding to Rita while simultaneously dealing with the fallout from Miguel's death and a new threat from George King. Dexter manages to kill George King after being captured and tortured. The episode concludes with Dexter and Rita getting married, unaware of a bloody drop falling from Dexter's cast onto Rita's wedding dress, hinting at future darkness.