Two escaped convicts are found hiding in a rocketship built by a renegade inventor, who forces them to become the crew for a trip to the Moon. Also on board, as inadvertent stowaways, are his assistant and his secretary; and none of them are aware that the inventor is actually a Lunarian explorer sent to Earth by the dying Lunar civilization and the only remaining male member of that civilization.

A mission to Venus discovers the planet inhabited only by women led by their evil Queen Yllana. Yllana had all the men of Venus killed, now that's she met Earth men, she wants them dead, too.