Barbara Terranova, a financially struggling woman, hires Magnum for one day to find her missing fiancé, Roger. The case grows complex as Magnum discovers others are also searching for Roger. Complications escalate when T.C., seeking publicity for Island Hoppers, pressures Magnum to compete in the upcoming swim-run-bike Ironman triathlon. Barbara, a fitness trainer, trains Magnum for the event in exchange for his continued help in locating her fiancé.