The Black Whale III reaches its destination, and the crew begins a scuba exploration of some underwater ruins.
A submarine earthquake disturbs the ruins and crushes the legs of Michelle Marvin, the family's eldest daughter.
The ship attempts to head for the nearby island of Bimini for help, but they become stuck in a storm, hit some rocks, and have their engines and helm damaged.
The ship's cook dies in an apparent accident during the storm, and Diana's parents are swept overboard looking for her.
At Bimini, the radar operator says that their story is implausible, for the Black Whale III disappeared about twelve years ago with a family named Marvin aboard.