When Magnum and old school private eye Luther H. Gillis encounter each other in a seedy hotel room with a dead drug dealer as they separately investigate the whereabouts of Nancy Perkins, a St. Louis runaway, they decide to team up to find the missing girl after the police burst into the room and arrest them on suspicion of murder.

Magnum reluctantly agrees to chaperone Rick's prim and proper 22-year-old sister and then finds himself trying to keep up with a wild hellion. The girl goes missing after dragging Magnum to a low-life nightclub, but things take an even more bizarre twist when the police find her murdered in an alley.