The owner of a five star London hotel leaves for a holiday, and to everyone's surprise promotes Old Mother Riley from kitchen dishwasher to manageress. Chaos ensues, and Mother Riley and Kitty are suddenly suspects in the theft of the Royal Hula Diamond, but somehow along the way, also manage a trip to a beauty parlour. a banquet with Arab royalty, some Saint Patrick's Day celebrations, and a climactic custard pie fight.
Kim Walker (Deanna Durbin) is an ambitious waitress who dreams of being on the stage. She tricks respected stage actor John Sheridan (Charles Laughton) into signing a letter of introduction. Thanks to the forged letter, Kim then wins the role of Sheridan's co-star in his next play, much to the disgust of the writer Paul Taylor (Franchot Tone).