'Dexter' season finale features killer surprise from Deb Randy Tepper/Showtime Michael C. Hall (Dexter Morgan), David Zayas (Angel Batista), Lauren Velez (Maria LaGuerta) and Desmond Harrington (Joey Quinn) on "Dexter." Warning: This story contains spoilers from "Dexter's" seventh season finale. With Dexter's walls closing in around him more than any previous of its six seasons, Showtime's famed serial killer with a code entered uncharted territory during Sunday's seventh season finale. The episode, which takes its "Surprise, (expletive) " title from James Doakes' old catchphrase, was a heart-racing hour in which Dexter attempted to tie up several loose ends. Among them: Hannah McKay (Yvonne Strahovski), who not only knows about Dexter's Dark Passenger but loves him because of it; Capt. Maria LaGuerta (Lauren Velez), who is convinced that Dexter (Michael C. Hall) is the Bay Harbor Butcher; and Hector Estrada, the last surviving man responsible for his biological mother's murder. STORY: "Dexter's" Jennifer Carpenter: Deb may end up "being the superhero" So how did the serial killer with a code fare? Turns out a lot better than his foster sister, Deb (Jennifer Carpenter) did. After LaGuerta frames Dexter in an attempt to catch him killing Estrada, Dexter returns the favor and frames Miami Metro's captain -- planting her fingerprint on Estrada's ID -- after she arrests him for murder and suspicion of being the Bay Harbor Butcher. With her career on the line for the "mistake," LaGuerta begins to clean house -- thinking that her days at the station are numbered -- and calls Deb in to go over newly returned evidence in Travis Marshall's (Colin Hanks) case from the church where Deb first witnessed Dexter's true nature. The security footage puts Deb at a gas station two blocks from the church just 22 minutes before it burned down, and LaGuerta begins to realize that Deb is covering for Dexter's role in the case that ended in fire. STORY: Can "Dexter's" Hannah and Deb co-exist? Yvonne Strahovski weighs in Shifting his sights to LaGuerta, Dexter discovers she has search warrants for the GPS calls from not only his but Debra's cell phones on the night of the church fire, proving that Deb was Dexter's accomplice in the fire that killed Travis -- and the blood slide that proves he has the same M.O. as the Bay Harbor Butcher. It's at that moment that Dexter realizes that he has no other option but to kill LaGuerta so Deb doesn't lose everything. Dexter ultimately catches Estrada (Nestor Serrano) before LaGuerta can and has him call LaGuerta and lure her down to the containers where Dexter's mother was murdered. "I've never killed for normal reasons," Dexter tells Estrada of the need to survive before he kills him. I used to think I was a special kind of killer but tonight, I'm not. After he kills Estrada and LaGuerta arrives, Dexter injects her with half a dose of his typical tranquilizer (so it wouldn't appear in her bloodstream) and just as he's about to set up the scene to reveal LaGuerta and Estrada shot and killed one another, Deb arrives and begs him not to kill LaGuerta, though she is unaware that LaGuerta had the smoking gun connecting them to the church murder and more. PHOTOS: Comic-Con 2012: 6 all-stars talk fans, mortifying auditions and how their shows should end at THR's roundtable It's at that point when LaGuerta wakes up. "This is not who you are!" she tells Deb. You're a cop, you're a good person, you're not like him! Put him down! And Deb does the unthinkable: She shoots and kills LaGuerta, thus making the ultimate sacrifice yet again to protect Dexter, and setting up a new set of questions ahead of the upcoming eighth season of the Showtime drama that viewers hear via Dexter's signature voiceover: Who is Deb now? Who is Dexter now? Is this a new beginning or the beginning of the end? Not to be outdone, Hannah escapes from the hospital after having ingested something her old friend Arlene gave her and leaves a flower on Dexter's doorstep and setting up yet another slate of troubles for the Morgans: Will Hannah kill Deb in order to be with her true love, Dexter? What did you think of Dexter's season seven finale?