When the proprietor of a posh London hotel mysteriously decides to take a break, he promotes Old Mother Riley straight from kitchen dishwasher to the head of the hotel! So it's goodbye Ration Row and hello swanky Penthouse living for Old Mother Riley and daughter Kitty. First stop is the beauty parlour – a real challenge – and then it's off to a feast with Arab royalty for a lesson in appalling table manners! However, there are sinister goings on at the hotel. The royal Hula Diamond goes missing – and Old Mother Riley finds herself accused of murder! To prove her innocence, she and Kitty must become crimebusters – armed only with custard pies from the kitchen! Joining her on her new venture is a great supporting cast which includes Sebastian Cabot and John Le Mesurier .