Few were disappointed when Raoul Vernet was found with his head bashed in, dead in a pool of his own blood. On vacation in England, the Belgian seducer comes to visit Matilda, an old flame from a few years before. She agrees despite suspicions that Vernet has been deploying his legendary charm on another member of the family: young Rosie, who has returned from her Swiss boarding school carrying a child.

None of the family members were in the house when Raoul was killed, but all were within a fog-choked London mile. Rosie calls in the brilliant Inspector Cockrill to clear the family's name, but what he finds is a twisted clan of seven people, each as likely to laugh at a murder as commit one.