Dexter Morgan investigates a double homicide at the University of Miami campus, where two female students have been found burned and beheaded. Their heads are replaced by the ceramic heads of bulls. Something about this uncharacteristically frightens Dexter's "Dark Passenger" into silence, leaving him to solve the crime on his own. As a series of similar murders take place, members of a mysterious cult begin stalking Dexter, believing his Dark Passenger to be a threat to them.

Dexter soon begins to question the Dark Passenger, as he slowly realizes that it's a true entity unto itself, possibly an offspring of the ancient god Moloch. While attempting to dispatch a killer who had been stalking him, Dexter becomes frightened and is unable to go through with the deed. He soon realizes that the Dark Passenger had given him an unusual amount of confidence and an almost supernatural awareness of the world around him; now that it's gone, he feels vulnerable for the first time in his life. Dexter begins to develop sadness and anger, emotions that were once suppressed by the Dark Passenger. While missing the helpful clues and hints of the Dark Passenger, Dexter feeds off of his newfound emotions to find some balance in his life as well as solve the mystery unfolding around him.