Dexter Morgan, a Miami crime scene investigator who is sometimes moved to commit murder himself--goaded by a reptilian voice he calls his Dark Passenger--gets a clue that something is very wrong when he is called to the scene of a double homicide at the university campus, only to have Dark Passenger go into hiding.

Dexter, a serial killer who limits his victims to other killers, bides his time between murders by working as a blood splatter analyst for the Miami Police Department, and dating Rita, the single mother of two children, but he is faced with a challenge when a psychopath arrives in town and his sister, a newly-minted Miami detective, becomes involved in the case.