Dexter Morgan (Michael C. Hall) will have a new nemesis for season four of the hit serial killer thriller Dexter - multiple Emmy-winner John Lithgow.

According to EW.com's The Ausiello Files, the 3rd Rock from the Sun star will play Walter Simmons, a gentle-seeming chap who relocates to Dexter's neck of the woods to escape pursuit by the FBI.

The reason: Walter is actually the Trinity Killer, a very prolific serial murderer who slays his victims in threes. FBI Special Agent Frank Lundy (Keither Carradine) is closing in, forcing Walter to move to Miami.

Dexter's fourth season will begin on Showtime in the United States on Sept 27. Lithgow has apparently signed on for all 12 episodes of the season.