In the South Pacific, 1000 feet below the surface, a space ship rests on the ocean floor - and it is at least 300 years old. Rushed to the scene are four scientists: an astrophysicist, a biologist, a mathematician and a psychologist. Together they descend into the depths of the sea to investigate. Has it come from an alien culture? From the future? What is the giant, perfect silver sphere - clearly not man-made - that they find inside the ship?