The young hotel manager Leutner runs for study purposes a transmitter in the hotel room of his fiancée Maria. Coincidentally he learns that a gang of counterfeiters want to get rid of a troublesome witness at 12:15 AM. Will Leutner be able to prevent this… and can he trust his fiancée at all? Cheats, swindlers, forgers and murderers are hiding under the mask of honest and reputable hotel guests.