What are the green glowing bubble creatures that the young scientist-inventor encounters in the depths of the Pacific Ocean? How do they rescue Tom and his pal Bud Barclay from an attack by the fish men?

Tom's electrifying adventures begin deep in the Mariana Trench where he has based his newest invention, the Dyna-4 Capsule, in a hunt for rare metals. A super submarine, the craft has been especially designed for deep-sea research and exploration.

On orders from Washington, Tom takes time out from his own project to recover5 a stolen vial containing a highly destructive explosive. The top-secret mission turns into a danger-filled whale chase in the Dyna-4 and leads to a showdown with Tom's ruthless foes.