While investigating a series of eerie threats, the TAU team discovers the victim's house has a creepy history and is believed to be haunted. When the danger turns deadly, the team spends Halloween night searching a wild costume party looking for a perpetrator long believed to be dead.

Stalker is a psychological thriller about detectives who investigate stalking incidents - including voyeurism, cyber harassment and romantic fixation - for the Threat Assessment Unit of the LAPD. Det. Jack Larsen is a recent transfer to the Unit from New York City's homicide division, whose confidence, strong personality and questionable behavior has landed him in trouble before - but whose past behavior may also prove valuable in his new job. His boss, Lt. Beth Davis, is strong, focused and an expert in the field, driven by her traumatic personal experience as a victim. With the rest of their team, young but eager Det. Ben Caldwell and deceptively smart Det. Janice Lawrence Larsen and Davis assess the threat level of cases and respond before the stalking and intimidation spirals out of control, all while trying to keep their personal obsessions at bay.