The Fioras jewels are missing and Francesca Lisle, one of John Mannering's (aka "The Baron"s') neighbours, is mysteriously asked by her father to retrieve a leather holdall from underneath the floorboards and take it to him at Waterloo station. Francesca is kidnapped, however, and ends up in the River Thames. Meanwhile, Joy Lessing is also kidnapped, or so it would seem. Mannering is unwittingly involved and sets off to investigate, but cannot tell the police everything he discovers.