Of the impressive list of [Mrs. Christie's] volumes, mostly about Poirot,… the best known and most widely discussed is the brilliant The Murder of Roger Ackroyd…. At the present late date it is betraying no secret to say that this remarkable story, a tour de force in every sense of the word and one of the true classics of the literature, turns on the ultimate revelation of the narrator as the criminal. This device (or trick, as the reader may prefer) provoked the most violent debate in detective story history. Scarcely had the ink dried on the pages before representatives of one school of thought were crying, "Foul play!" Other readers and critics rallied as ardently to Mrs. Christie's defense, chanting the dictum: "It is the reader's business to suspect every one." The question remains unsettled to-day, and the inconclusive argument will probably continue as long as detective...