The working title of this was London Particular: first published in 1953, it's a whodunnit, of which the murder takes place on a night when London's drowned by one of the old pea-souper fogs.
Raoul Vernet is a Belgian, visiting his old flame Mathilda, who's now married to a doctor named Thomas. Thomas's teenaged sister Rose has just confessed that she's pregnant, though she tells a different story to each listener: Mathilda, the live-in help Melissa, her Gran old Mrs Evans (much given to reenactments of desert abductions, and to chucking cushions out of the window), and to Thomas's partner in practice, Tedward. And lurking around the scene are two additional male suspects, the mysterious Stanislaus and the somewhat less mysterious Communist Damien.
The pieces are cleverly put together and the novel kept me guessing -- this was a one-sitting read -- and the characters all came to life, though in a rather dated way that's only to be expected given the book's vintage. It's a good portrait of middle-class life in 1950s London -- assignations in phone boxes, the difficulties of locating an address before the A-Z of London streets was available, the options open to an unmarried mother before abortion was legal: and it's a very competent and tightly-plotted murder mystery, though I found myself losing interest and patience towards the end.