At the Nelson Institute, Admiral Nelson oversees a deep dive experiment conducted by the submarine Polidor, manned by a hand-picked crew. After a short time, the Polidor crew panics, sending the sub too deep, where she explodes. Wracked with guilt, Nelson becomes obsessed with discovering the cause of the tragedy. A committee appointed observer, psychologist / scientist Dr. Arthur Kenner, is the inventor of a fear gas, which was used without his knowledge to send the Polidor crew to their deaths. His assistant Martin Davis joins him on the expedition. Davis, however, is a spy, and has brought a container of fear gas with him, releasing it into the air revitalization system.