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 letter summons American detective Steve Marshall to Sao Paulo, Brazil, in search of fugitive murderess Louise Dunning. Marshall contacts Louise and learns that she murdered her husband only in self-defense. In the meantime, Marshall is set up as a pawn in a counterfeiting ring (they were the ones who sent him the letter), and unwittingly helps the police capture the criminals. Louise decides to remain in Brazil.
Dr. Frankenstein's insane grandson attempts to create horrible monsters in modern day L.A.
