Having been caught in the act of eliminating Travis Marshall by his sister Deb, Dexter has to scramble to come up with an explanation. Deb is understandably shaken by what she's just seen but accepts, somewhat reluctantly, Dexter's explanation that he's suffered momentary madness. As she thinks about it, Dexter's explanation makes no sense and decides to dig deeper. Captain LaGuerta meanwhile is puzzled by a piece of evidence she found at the scene of the Marshall killing. When a member of the homicide squad is killed, Dexter goes all out to stop the killer before he ...