The US Government is very smartly letting Tom Swift Jr. handle the recovery of its probe to Jupiter. But a mystery missile suddenly intercepts the probe and splashes it in the South Atlantic.

Faced with a huge search task to find the probe on the ocean bottom, Tom soon realizes that the same shadowy group that attacked the probe is competing to find it, and no holds are barred: kidnap, coercion, and lethal force are all in play.

Under such circumstances, what can Tom do? What he does every time, of course! He invents some utterly cool device to get the job done! And his Electronic Hydrolung is just the beginning!