A new threat appears in Miami in the form of the Doomsday Killers (or DDK), Professor James Gellar and his student Travis Marshall, who seek to bring about the end of the world through killings based on the Book of Revelation. They leave signs of the Apocalypse including the Alpha and Omega or the Four Horsemen as a cryptic tableau at each crime scene. Meanwhile, Dexter learns of Brother Sam, a former drug addict and murderer who repented and became a minister. He operates a body shop where he employs other ex-convicts, to lead them to crime-free lives.
