Near the end of the war in Germany, GI Steve Boland, a self-described "sharp-operator", meets a German girl, Ilsa, and they fall in love. Ilsa's brother Karl, whom she has not seen in three years, and his fellow Nazi Ludwig visit Ilsa. Karl proudly informs her that he and Ludwig are "Werewolves", a group of Nazi assassins parachuted behind Allied lines for the purpose of killing Allied High Command officers. She and Steve go to Army Intelligence with their information, where Steve is immediately arrested for being A.W.O.L. Captain Melton of Army G-2 intervenes on Steve's behalf, as G-2 has had a suspicion about the existence of the "Werewolves" but no concrete info before now.

An American reporter in Japan is sent to interview an eccentric Japanese scientist working on bizarre experiments in his mountain laboratory. When the doctor realizes that the hapless correspondent is the perfect subject for his next experiment, he drugs the unfortunate man and injects him with a serum that gradually transforms him into a hideous, two-headed monster.