Crane is caught up with a circle of spies as he tries to make his way back to Seaview with important missile defense data.

Cruising for days under the ice, Seaview surfaces to find the sky is ablaze thanks to the Van Allen belt catching fire. Nelson races to Washington to confer with fellow scientists and hatches a plan to detonate a nuclear device into the atmosphere and extinguish the fire. Weber, a Fellow scientist, feels they should do nothing and allow the fire to burn out. Nelson disagrees and takes Weber and two others aboard Seaview to decide the course of action as the sub races to the firing point. However, Weber is determined to stop Nelson and is willing to kill to do it!

As World War II draws to a close, a secret underwater Nazi base is damaged during a sea battle. A Nazi scientist and his aide are accidently put in suspended animation. Thirty-five years later, the crew of the Seaview discovers and revives them. The Nazis attempt to carry out their interrupted mission: destroy the capital cities of the Allies.

Arctic Listening Station XZ-5 receives a message from a voice from space (""laser beeeeeam""). Professor Bergstrom, ignoring the advice of his assistant, activates their beam and brings the alien, living flame, to Earth. Now, this Heat Monster wants the Seaview to detonate a bomb under the polar ice cap. How can the intrepid crew defeat this new menace?

The Seaview crew is being entertained by puppet cairactures of the Captain and Admiral, compliments of Professor Multiple. Multiple remains on-board when the sub departs, and his dolls soon come to life, replacing their real-life counterparts. Only Nelson and Crane avoid capture and transformation. Multiple boasts that he and the others are all puppets, created by machines from the future that have traveled into the present, and need the Seaview as a new host body. Can Nelson and Crane overcome this fantastic threat?