As part of a military exercise, a breakthrough computer has been installed aboard Seaview
. The inventor claims this machine can run the ship entirely. Captain Crane is alone aboard ship, a token crewman so that the ship is not regarded as a derelict under maritime law. Or is he alone? An enemy agent has somehow snuck aboard, with a tape to reprogram the computer; if his mission succeeds, a hostile foreign power will gain control of Seaview
long enough to steal the secrets of the machine!