While honeymooning in Budapest, young couple Peter and Joan Allison meet Doctor Vitus Verdegast, who is en route to the mansion of his old 'friend', Hjalmar Poelzig. Forced to enjoy Poelzig's hospitality themselves following a bus crash, the Allisons discover that he is in fact a devil worshipper who betrayed Verdegast and thousands of their countrymen during WWI. Verdegast now wants revenge - but Poelzig pre-empts him by taking his guests prisoner, announcing his intention to turn Joan into the bride of Satan.