Lieutenant Maria Esperanza del Alma LaGuerta Batista is a tough, determined woman in command of the Homicide division who is not above making her subordinates feel intimidated. At the series' beginning, she had a sincere dislike for Debra which in later series has all but disappeared.[6] In the first season, she made no secret of her attraction to Dexter, with whom she flirted constantly, to his discomfort (which after the 1st season it is suggested that she sees him more as a good friend). At the end of the first season, she is removed from command, but returns to her old job once the new Lieutenant, Esme Pasquale, proves to be unstable (a state she contributes to by having an affair with Pasquale's fiance). When her friend, former partner and former lover James Doakes becomes the prime suspect in the Bay Harbor Butcher case, she tries to clear his name. She learns from a questionable source of two Special Forces missions Doakes took part in that directly conflicted with the deaths of two Butcher victims. However, Doakes is found dead in a seemingly accidental explosion, along with the body of drug dealer Jose Garza, and the case is closed. The evidence LaGuerta finds is ignored. After his death, LaGuerta starts a memorial fund for him, asking police officers for donations, and refuses to think of her deceased friend as a serial killer. As she recovers from the trauma of Doakes death, she leads an investigation into the murder of Oscar Prado, the brother of her ex-boyfriend Miguel Prado. She also develops a close relationship with lawyer Ellen Wolf, and is devastated when Wolf is found dead. But through the help of some personal investigation work, along with Dexter's help, she was able to discover that Miguel was the one who killed Wolf and usually confides in Dexter as he is the "only other one who knows". She becomes distraught when the Cuban community is thinking about naming a highway after Miguel and wants to find legal evidence to prove he killed Wolf, but Dexter is able to convince her that doing so would only hurt Miguel's family and the Cuban Community and even then there is a high chance that nothing will be proved, and LaGuerta drops it.

At the start of season 4, she is shown to be romantically involved with Angel, however this fact is kept hidden from the rest of the staff within the homicide department. Though she wishes to at least tell the higher office so their romance cannot be used against them during a trial. As of "Hello, Dexter Morgan", they secretly get married with Dexter as witness.

Her characterization in the show departs significantly from that in Darkly Dreaming Dexter, in which she is a shrill, manipulative woman whose only real objective is promotion within the department. Another departure from the books is that LaGuerta died near the end of the first book after being stabbed by Brian upon discovering Brian and Dexter standing over a restrained Deb. She is ultimately killed by Dexter's brother. While attending Maria's funeral, he mentions that all that's left of her is the blood slide in his pocket.