Martin Edwards describes his book as a homage to the Golden Age of English detective fiction, which flourished in the inter-war years and is best remembered in the works of Agatha Christie and Dorothy Sayers. The book is accordingly a pastiche: a country house murder/mystery set in Yorkshire (with some preliminaries in Soho) in 1930, written in the style of the Golden Age and using all the tropes, stock characters and conventions of the genre. Indeed it is so over-the-top that I am not certain if this is meant to be a parody.
Not that it is easy to parody a Golden Age murder/mystery. They were never meant to be realistic. The world they created is as much a fantasy as Tolkien. They are puzzle pastimes, a product of the same age which invented crosswords. Edwards even provides a ‘cluefinder’ at the end of his book, in case you missed any of the clues hidden in the text.
Mortmain Hall is a remote Victorian gothic country house to which the mistress of the house (the owner being an invalid from the Great War) invites a mixed group of well-to-do people for the weekend, each of whom has a motive for murder. In the event there are two murders, not to mention an earthquake, and the astute lady detective who is among the guests unravels the mystery and convenes the survivors in the Library to unmask the killer. Needless to say it is not one of the chief suspects.
A pleasant piece of entertainment on the sillier side of the Golden Age.