Season 3 opens with Dexter tracking a killer who got away with murdering two college women, and winding up in a life-or-death struggle with a stranger who is in the wrong place at the wrong time. Debra investigates a high-profile homicide and gets pressured by an Internal Affairs officer, who wants her to snitch on a fellow cop; Angel gets good news about his career; Rita startles Dexter with some news of her own.
Something's gotta give when Debra and the homicide unit, ADA Miguel Prado (Jimmy Smits) and Dexter all chase the same serial killer, who murdered Prado's younger brother. On the home front, Dexter's faced with a big family decision involving Rita and her two children.
Dexter has a run-in with a pedophile; Freebo is accused of a murder he didn't commit, and Dexter knows the truth but can't say anything about it. Also, Dexter's friendship with Miguel begins to weigh on his mind.
Ramon's obsession with finding Oscar's killer has him putting his career at risk, and Dexter does a masterful job manipulating Ramon and keeping him off balance; Internal Affairs leans harder on Deb to dig up some dirt on Quinn, but she "won't be a rat." Also, Rita and Dexter decide to tell the children about her "condition," and Angel's quest for companionship nearly gets him in hot water.
Rita wants Dexter to move in with her and the kids before they wed, but he's confused about it; Miguel tips Dexter about a husband who's gotten away with murdering two wives for the financial windfall, and Dexter ends up tracking him to the Bahamas; Debra becomes attracted to a confidential informant who is helping her track down one of Freebo's partners in crime.
Dexter suspects that Miguel is on to his dark-side job and decides to test him; Rita gets fired from her job and begins to question her career path; Debra thinks she somehow contributed to another homicide that's related to the case she's working.
Miguel targets a new victim for Dexter, who's not so sure the new target lives up to (or down to) Harry's Code. Meanwhile, an elderly, deathly ill friend of Dexter's asks him to assist in her suicide; Rita learns that Miguel's wife thinks he's having an affair; Debra lets on to Anton that he's being used as a decoy to nab the Skinner.
Miguel not only brings Dexter another potential target but wants in on the action; Rita's pregnancy causes her to fear that Dexter will lose interest in her; Debra's digging gets her closer to nabbing the Skinner, and upon discovering a secret about her new boyfriend, Anton, he disappears.
Rita's intention to confront Miguel about his alleged infidelity has an impact on his friendship with Dexter; Debra pulls out all the stops to locate Anton after it is believed that he's been abducted by the Skinner.
Dexter and Miguel engage in a series of manipulative moves in an attempt to gain the upper hand; Miguel ingratiates himself further into Rita's good graces by gifting her with an expensive wedding present; Debra questions whether her relationship with Anton is heading anywhere.
Dexter preps for his wedding day but must first divorce himself from Miguel, which proves most difficult as Miguel is a prominent D.A. and Dexter's best man. Sylvia confides in Rita that Miguel has been seeing an ex-lover; Debra digs up new clues in the Skinner case.
Miguel's out of the picture, but his unstable brother Ramon still poses a threat to Dexter; a potentially fatal surprise could imperil Dexter's impending nuptials to Rita; Debra learns she's in line to get her detective's shield, but troublesome news could tarnish her promotion.