Dexter faces a serial killer from his past; Debra has problems with her new position and Travis with Gellar think of their next move.

With the help of his newfound friend Brother Sam, Dexter wonders if there is light within him to counter the darkness, while the search for the Doomsday Killers takes him in a new direction; Batista and Quinn pay a visit to the university where Professor Gellar taught; due to departmental regulations following the shooting, Debra is forced to begin therapy.