On its maiden voyage, the crew of the Seaview discovers that the Van Allen radiation belt encircling Earth has caught fire. With the planet's temperature rapidly climbing, Admiral Harriman Nelson (Pidgeon) knows the only way to stop the burn is to fire a nuclear missile into the belt from a specific location, releasing the radiation into space. To reach the launch site, he'll face enemy subs, a hypnotizing mutineer and even a giant squid, but will he make it in time to save the world from going up in smoke?