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.
Magnum dons his sailor's cap when a young marine biologist hires him to take on supposedly cursed waters and find out what happened to her missing archaeologist father.
- Tom Selleck as Thomas Sullivan Magnum IV
- John Hillerman as Jonathan Quayle Higgins III
- Roger E. Mosley as Theodore "T.C." Calvin
- Larry Manetti as Rick Wright
- Jeff MacKay as Lieutenant McReynolds
- Wendy Girard as Marion Hammond
- Ina Balin as Professor Martinez
- Mamaluna as Tehani
- Curtis Malia as Keone
- Roger E. Mosley is credited, but does not appear.
- The "Nihoa Channel" does not exist. Nihoa is a remote, unpopulated island in the Northwest Hawaiian Islands, but there is no channel named for it, nor any island close enough to form a channel.
- The conversation about figments of the imagination would inspire Disney Imagineer Tony Baxter to assign the name Figment to the dragon character in Epcot's Journey into Imagination, seeing an opportunity to visualize the word.