Ben Sullivan (Callum Keith Rennie) is a tough, smart homicide detective with Multiple Personality Disorder. In the first moments of the series, Ben and his new partner Amy Lynch (Camille Sullivan) pursue a murder suspect and Lynch is forced to shoot. The resulting SIU investigation bonds the two partners in blood. Each week they work to solve the murder cases that cross their desk daily, while Ben copes with the fascinating complexities of managing his life as a cop while living as a man with alternate personalities and the uncertainty of never knowing which personality will surface. Or when.