Bestseller Hannah’s third Hercule Poirot pastiche (after 2016’s Closed Casket) offers Agatha Christie fans another ingeniously deceptive puzzle. The premise is especially clever-someone, posing as Poirot, has sent letters to four people accusing each of them of having murdered Barnabas Pandy. Pandy, a 94-year-old, was found drowned in his bathtub in Combingham Hall three months earlier-a death that was universally accepted as a tragic accident. Two of the recipients of the letters confront Poirot angrily, professing to have no idea who Pandy was, but the third, Annabel Treadway, distraught at the accusation, discloses that Pandy was her grandfather and insists that no one in the household could possibly have killed him. Aided again by Insp. Edward Catchpool, an enigmatic Scotland Yarder, Poirot uses his “little gray cells” to ascertain who has been impersonating him, whether Pandy was in fact the victim of foul play, and if so, whodunit. The gratifying reveal is a neat variation on one of Christie’s own solutions and demonstrates Hannah’s facility at combining her own plotting gifts with another author’s creation.