Magnum has been hired by a woman to act out some of her rich, bored sister's fantasy dramas, concocted from 1930s Dashiell Hammett films, but soon finds himself involved in a real mystery.

Magnum is hired by Barbara Terranova, a near-bankrupt woman who can only afford his services for one day, to find her missing fiance, Roger, but she's not the only one searching for him. Meanwhile, T.C. gets Magnum to compete in the Ironman triathlon to give Island Hoppers some publicity.