In a boarding house off the Pimlico Road run by a Mrs. Petter, one of the guests, Julia Keene, is taking her leave after staying there for a short time. Mrs. Petter's daughter, Florrie, having seen Julia leaving a posh cocktail party in a house in Mayfair, wonders why the lady has been lodging with them. Florrie has elaborate and fanciful suspicions that Julia is involved in a gang of cat burglars and her job is to stake out the territory ahead of the other gang members. Florrie's mother scoffs at her daughter's ideas.