It is a beautiful night for a gala and the Banfield family is hosting one with two hundred guests attending. The Banfield has a long history of honorable service in support of the Crown in all corners of the Empire. However, the present generation is squabbling since patriarch Lewis married Arlette the model he loves.

Lewis' Aunt Geraldine, the former mistress of the manor, dislikes Arlette because the woman didn't belong to their social circle and the woman's business activities reflect poorly on the family name. Other people also dislike Arlette with some jealous of her new status. Especially loathing the interloper are the Bickleton matriarch who don't receive a pound to repair their furniture thanks to Arlette.

However, others hated her too; only one person put poison in her champagne. Inspector Weatherspoon investigates the case while his housekeeping staff led by Mrs. Jefferies conduct their under the stairs inquiry unbeknownst but in support of their beloved employer.