A drifter named Magnus returns to his home in Bermuda (which he left after his father was mysteriously killed years before) and is reunited with Eric, an old friend who is learning about marine biology from an old scientist named Dr. Paulus. They end up investigating evidence of a giant turtle inhabiting the local waters.
Magnus also meets a mysterious, beautiful woman named Jennie Haniver, who turns out to have been a childhood playmate of his; in fact, hes still wearing the seashell necklace she gave him. The thing is, she only appears when hes alone, and even Eric tells Magnus that they believed Jennie was just an Imaginary Friend of his. He insists that she was real, and that he even carved his and Jennies initials on the back of a turtle they played with.
Erics wife explains that Jennie Haniver is a local Urban Legend: Two hundred years ago, a young woman whose ship sank in a storm in the Bermuda Triangle made a Deal with the Devil so that she would survive. Naturally Magnus refuses to believe it is the same Jennie.
Eric becomes obsessed with catching the giant turtle and against all warnings uses a harpoon cannon on it. This just leads to the creature killing him and Dr. Paulus. Jennie is revealed as indeed being supernatural in the process.
Tropes in The Bermuda Depths:
- Bermuda Triangle: One of the oddest takes on the legend: It was a giant turtle demon.
- Black Best Friend: Eric
- Boy Meets Ghoul: It is never exactly clear what Jennie was—ghost, cursed immortal, etc.—or why she first appeared to Magnus as a little girl.
- The Drifter: Magnus
- Eaten Alive: Magnus' father, apparently for finding evidence that the turtle demon existed.
- Glowing Eyes of Doom: Both Jennie and The One Below show them.
- Hoist by His Own Petard: Eric dies yanked underwater by the harpoon line.
- Keep Circulating the Tapes: For a long time, even the very existence of the movie was in doubt and copies were very hard to find.
- Too Dumb to Live: Eric
- Who Wants to Live Forever?: Jennie came to regret her pact but cannot escape it.