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.

While Magnum prepares for an annual surf-ski race, Higgins has his hands full hiding the beautiful Lady Wilkerson from two shady pursuers. Smitten by the maiden in distress, Higgins sends her a letter expressing his feelings, but she mistakenly thinks the amorous words are from Magnum. It quickly becomes a case of romance on the run when the duchess is kidnapped and the two "Romeos" must spring into action to save her.