It is the relationship between Dexter and Debra that leaves a big question mark in the season 6 finale of "Dexter". As if Deb's growing feelings to her adoptive brother are not complicated enough, she now has to [SPOILER ALERT!] deal with a shocking fact that the man she loves is a serial killer.
In the season ender, Dexter managed to convince Travis to switch his son Harrison with himself as a sacrifice. He pretended to be drugged and then knocked out Travis when he got the chance. He later took Travis back to the church, in which Travis set up shop, and got him on his table.
Elsewhere, Deb met her therapist once again to say, "I finally told my brother that I love him and he said he loves me back!" Deb, however, thought that Dexter does not understand her true feelings. She then followed her therapist's advice to profess her romantic feelings to him.
Deb headed to the church since she had earlier assigned Dexter to visit the place for a final sweep. Unfortunately, she came just in time to witness her adoptive brother stabbing Travis in the heart. "Oh God," the serial killer said when he noticed Deb's presence.
Dishing on how the ending in season 6 sets up the possibly final two seasons of "Dexter", executive producer Sara Colleton has said, "We want to lay the groundwork to have the most interesting way into examining how Deb will react."
She explained, "If we hadn't evolved Deb, then there could only be one reaction, which is horror and arrest, and end of story, which indeed may be the case. It just allows us to have a more complicated character who has to deal with it in a more nuanced way."