Magnum, P.I. (1980): Season 4, Episode 4

4 - 4: Distant Relative

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.