At the Pentagon, Navy officers and scientists are stumped. Two scientists mysteriously disappeared in Antarctica. They call in "men capable of handling the unknown." Ace, Rocky, and Red fly off, picking up Prof along the way. Off New Guinea, Prof is astounded to find a volcano rising from the sea bed. In the Antarctic, the Challengers snow-tractor toward the mystery spot. The tractor bogs in a snowstorm and needs repairs. Ace and Rocky explore and fall through thin ice! They land on a futuristic bridge. Above, Prof and Red are captured by skinny orange aliens in bubble-suits.; Two captured Challengers are dropped down a miles-deep airlift. Ace and Rocky find an airshaft and search for miles. They reach a underground city of aliens with an army preparing for invasion. Ace tries to capture a sentry, but the alien anticipates his every move with its computer-like mind. All four Challs are imprisoned with the missing scientists. The aliens are planting charges all over the world to blow away chunks and reduce Earth's mass intending to enslave the human race. Prof realizes the undersea volcano was a test. The Challengers plan to attack when the aliens are at rest.; The Challengers hypnotize an alien who leads them to a gravity control room. The team crank the gravity high, pinning the aliens to the ground. Ace and Rocky try to destroy the main detonator. Prof and Red teleport to Washington and alert the military who bring their forces to the battle. Prof is given a wearable minisub and attempts to dismantle the bomb. Underground Ace, Rocky and the two scientists flee a gas attack and gun-cars. Cranking a valve brings raging heat that crisps aliens and slags the bomb detonator. In the Pacific, a claw-machine erupts from the ocean to attack the Navy.; On the Pacific island, Red sprays a new secret chemical weapon, a corrosive gas that eats the machine. Soon Ace leads a fleet of bombers to pound what's left of the alien base, and the menace is over. Their only casualty is Prof, who caught a cold diving off the South Pole!