When Scotland Yard's Henry Tibbett starts getting mysterious crossword puzzles in the mail, he soon deciphers the clues (with help from a crossword-maven Bishop)--and realizes that he's being joked with by the members of the ""Guess Who Club,"" mystery-writers with pseudonyms who have invited him to their upcoming annual get-together. But once Henry and wife Em arrive at the Guess Who gathering, held at the manse of publisher Sir Robert Oppenshaw on the Isle of Wight, he wonders if the crossword solutions (which kiddingly hinted at murders in the mystery-writers' pasts) should be taken seriously. . . especially when young Peter Turnberry, fiancÃ‰ of Oppenshaw's daughter Barbara (a Guess Who writer herself), is found dead in a ravine. A horse-riding accident? Henry thinks not. (Peter was about to spill some secret.) And, while another member of the Guess Who Club (an Oxford don) disappears under odd circumstances, the Tibbetts start looking closely at each of the writers--and into the past of publisher Oppenshaw--before coming up with the somewhat Christie-ish but over-gothic (and longwinded) solution. Middling fare from the erratic Moyes--with a rather gnarled plot, not enough Em. . . but considerable charm, atmosphere (an Isle of Wight travelogue), and English geniality.