It's 1956, and Lee Plunkett has taken over the family business as a private investigator despite his reluctance to follow in his father's footsteps. When murder intrudes on a group of ghost seekers, Lee is asked to solve the case by a cop on the verge of retirement. At the urging of his perpetual fiancée Audrey, Lee enlists the help of Mr. O'Nelligan, a scholarly Irishman with a keen eye for solving mysteries. The duo is drawn into a murder investigation involving the "Spectricator," a machine designed to communicate with the dead. Soon, Plunkett and O'Nelligan are knee-deep in a suspect pool that includes a surly medium, a former speakeasy queen, a mysterious Spanish widow, and a whole slew of eccentric servants.