When nuclear war breaks out and the nations of the Earth are destroyed, a group of US astronauts are marooned on the lunar surface. Using the "torsion field generator", a WWII Nazi Wunderwaffe previously known as the Bell, they hope to find an alternate Earth that did not suffer nuclear Armageddon. But once they do discover one, how will they return home? They have a single Lunar Module, which can carry only four astronauts into lunar orbit.