John Dickson Carr's The Eight of Swords (1934)

 "Ma'am," said Dr. Fell urbanely, "one of the most unfortunate features of police work is that it brings us into contact with people whom we should otherwise run a mile to avoid.  Pray accept my assurance, ma'am, that nobody appreciates this more than I do."                                                                       -- John Dickson Carr, The Eight of Swords (1934, republished by Penzler Publishers 2021)

The so-called "golden age of detective fiction" never really existed, unless one thinks that English writer Agatha Christie has a great deal in common with Americans Erle Stanley Gardner and John Dickson Carr; as a splitter rather than a lumper I don't see it.  Most of Carr's novel's do take place in England, but usually include a certain level of subdued American irony.  The Eight of Swords is the third of twenty-three books with detective Dr. Gideon Fell, who looks rather like G.K. Chesterton, author of the Father Brown novels.  This is not a locked room mystery; indeed there are many open doors and windows to the room where Nick Depping was killed and no one in the neighborhood seems to have a motive.  But Fell begins to figure out that not everyone is who they claim to be; Depping himself has something of a secret past and was even known to wear a disguise at one point the night he was killed.  There are poltergeists and bishops sliding down banisters, crooked lawyers and incompetent police, writers and servants, attractive young ladies and dowdy old wives.  Fell gradually sorts it all out as two additional murders take place during his investigation while Fell narrows down the dwindling number of suspects.  As Fell concludes, "the one-little-damning clue was a large and many-caloried dinner, steaming before your noses."