<-- Previous EpisodeNext Episode -->
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!
If the foreign power knows enough about this computer to reprogram it, why do they need to steal it? The answer might be that it uses a more-or-less standard programming interface to control unique and highly advanced hardware. Or it might be that there is a spy somewhere on Reston's team who was able to steal the programming interface, but nothing else.