Dexter: Original Sin will air in December 2024, and it'll feature a star-studded cast, who will play a mixture of new and original characters in Dexter's origin story. Sarah Michelle Gellar will play CSI Chief, Tanya Martin, who is young Dexter's boss. Gellar will be a special guest star in the first season, and this has many fans speculating about what her actual role could be in the prequel series.