The novel follows a psychologist named Norman Johnson, who is called by U.S. Navy to join a team of scientists assembled by the U.S. Government to examine an enormous spacecraft discovered on the bottom of the Pacific Ocean. The depth of coral covering the craft proves that it has been lying there for over 300 years and so could be of only alien origin.
The novel begins as a science fiction story, but quickly transforms into a psychological thriller, ultimately exploring the nature of the human imagination.