Night falls in London, and a ‘London particular’ pea-souper fog envelops the city. In Maida Vale, Rose and her family doctor Tedwards race through the dark after a man has telephoned claiming that he has been struck by an assailant in Rose’s house. Arriving after an achingly protracted journey through the impenetrable fog, the victim, Raoul Vernet, is dead. The news which he had brought from Switzerland for Rose’s mother was never delivered.

Seven suspects had the opportunity – though their alibis are muddled by the obscuring blanket of fog – but who among them had a motive? And as friends to each other, would every one of them claim responsibility to protect another? Inspector Cockrill – also a friend of the family – has a fiendish case ahead of him as his young rival Inspector Charlesworth joins the investigation, keen to see justice done for this unusual murder.