Billy Joe Bob, a hotheaded Texan, engages Magnum's services when his sister, Carol Ann, goes missing. Magnum has his hands full trying to keep Billy Joe from beating up every local who gets in his way and trying to find Carol Ann, who has gotten in over her head with the wrong crowd.
After her archaeologist father's boat is found deserted at sea in the Nihoa Channel, a marine biology student hires Magnum to find out what happened to him. The local natives warn Magnum to stay away from the "cursed" channel, but he's determined to find out what happened to the missing man.
Sara Clifford committed suicide in the Summer of 1945 by driving her car off a cliff. Rick meets a woman dressed in white named Sarah in the King Kamehameha Club but when they go for a walk on the beach, the woman disappears.
Magnum thinks he's spotted his one true love Michelle, the woman he married six years earlier during his last tour in Vietnam and thought to have been lost in a bombing raid. As he becomes more and more desperate to find her, he is suddenly and suspiciously recalled for active Navy duty and ordered to testify in Washington.
The infamous daredevil and author 'Mad' Buck Gibson parachutes on to the beach near the club. Joan, one of his ex-wives, hires Magnum to keep an eye on Buck to make sure she collects her alimony. Although Magnum can't stand the idea of being a babysitter, Gibson leaves a trail of destruction behind him that sees both Higgins and Rick end up in hospital.
Dick McWilliams, an old military buddy of Magnum's has been kidnapped. Dick's Japanese wife Mitsu ask TM to drop the ransom without informing the police or her father, who never approved of the marriage in the first place.
Magnum is searching for a spy who's been selling computer information from a large corporation. The president of the company tells him he suspects his wife of having an affair and asks him to follow her. Magnum is distressed to find her having an intimate dinner with one of his best friends, Rick.
The Ferrari, with an unconscious and injured Magnum in it, is found at the bottom of a cliff. Magnum is rushed to a hospital but when he regains consciousness is found to have amnesia and cannot remember what happened.
Someone is trying to kill professional football quarterback Dorsey Bramlett who was the backup quarterback for Magnum at the U.S. Naval Academy. Bramlett contacts Magnum and asks Tom to be his bodyguard.