Janis Bellacrest (Helen Parrish) books Kay Kyser (Kay Kyser) and his big band to play at her 21st birthday party. Between performances, Kyser has a series of disturbing interactions with Bellacrest's bizarre guests, including quirky Aunt Margo (Alma Kruger), pretentious professor Fenniger (Peter Lorre), creepy Prince Soliano (Bela Lugosi) and irritable Judge Mainwaring (Boris Karloff). When a powerful storm blows in, Kyser and Bellacrest begin to suspect something treacherous is afoot.