Chip Morton and Curley Jones are in New London making repairs on the diving bell's guidance system. At the same time a skirmish in the control room of the Seaview inadvertently allows it to move into a derelict mine field. The sub becomes entangled and attempts to free itself, but an explosion disables the sub and sends it to the bottom. With the crew running out of air the diving bell is their only hope.
—tomtrekp