The Twenty-Third Man by Gladys Mitchell

Dame Beatrice Bradley has taken a refreshing sea voyage to the island of Hombres Muertos where she plans to take a little holiday and watch the lizards sunning themselves in the garden of her hotel.  The island gets its ominous name from a cave which houses the mummified bodies of twenty-three men, all seated upright around a table and arrayed in masks and robes.  Dame Beatrice's fellow guests at her hotel are an odd lot: Caroline Lockerby, whose husband has recently found that pub crawls and Teddy-boy gangs are a fatal combination, and her highly nervous brother Telham; Mr Clun, just released from prison after serving a sentence for manslaughter; Karl Emden, an energetic lothario; and the occasionally resident Drashleighs, who are bringing up their adopted son Clement on a neighbouring island, using those free-thought educational methods soundly mocked in any number of twentieth century novels. 

Then there are the residents, the frankly bonkers Mr Peterhouse and sinister Mrs Angel, reputed to be a white slave trader with links to Buenos Aires; Senor Ruiz and his virtuous daughter Luisa, who own the hotel; and the rest of the islanders, including a group of villagers who live in cave houses and some curiously moral bandits.  Dame Beatrice's restful holiday is disrupted when Karl Emden is discovered in the cave of the Dead Men, taking a mummy's place at the table and wearing his robes and mask, and with a knife protruding from his back.  There are too many possible suspects, and Dame Beatrice has to return to London to find the roots of the murder in the earlier lives of Caroline, Telham and Clun.  Her perky assistant Laura takes her place on Hombres Muertos, bringing her small baby, who proves to be a useful means of getting people to talk to her.  Between them, the two women unravel the mysteries of the island and of Emden's death.

I've never read any Gladys Mitchell novels before and this was rather like a Golden Age murder mystery as written by Ivy Compton-Burnett.  There is lots of dialogue and little exposition; characters move from the hotel terrace to the beach in the turn of a paragraph, with no description of how they climbed down the steps or dawdled on the terrace. There is also a lot of rather arch humour; Dame Beatrice is witty and sharp, and Laura is permanently amused by the assumptions people make about her.   The mystery unfolds as Dame Beatrice thinks about the evidence she uncovers, but we are not party to all her thoughts and assumptions, so the mystery is sustained until the end.  This was pretty light but enjoyable and the style, which effaces clues rather than revealing them, kept me on my toes. 

This book is available, with several others, as a Vintage paperback; there are a few other reprints out there as well.  Gladys Mitchell wrote sixty-six books in her long career, so there is plenty of choice to sample from.  Incidentally if you enjoyed the highly frivolous Mrs Bradley Mysteries, made by the BBC a few years ago, Diana Rigg's incarnation of the character seems not to bear much resemblance to the Mrs Bradley on the page, although she is an equally enjoyable creation.