but whereabouts unknown) is somehow among the team. Two men - epigraphist Father Lavigny and drug-addicted historian Joseph Mercado - are the right age to be Frederick. Furthermore, three younger men - dig assistants Bill Coleman and David Emmott, and photographer Carl Reiter - are the right age to be William. Reiter in particular is of German-American ancestry, and was tormented by Louise for his shyness and clumsiness. However, he seems to have an alibi. Poirot is also intrigued to find that the letters Louise received were apparently in her own handwriting. Following Louise's funeral, Nurse Leatheran meets with Miss Johnson on the compound's roof. Johnson claims she knows how someone could have entered unseen, but does not elaborate further. That night, Miss Johnson unwittingly drinks a glass of hydrochloric acid which had been substituted for her usual glass of water on her nightstand. Amy attends to Miss Johnson, and hears her mention "the window" before she dies. The nurse does not believe Miss Johnson has committed suicide, and wonders if she hinted at how the acid was switched for the water. After spending a day sending telegrams, Poirot brings everyone together and reveals that both women were murdered by Dr Eric Leidner, who is, in reality, Frederick Bosner. The real Leidner died in the train crash 15 years ago - when Bosner came across his body and found his face disfigured, he switched their identities to escape the authorities. Bosner was deeply possessive of Louise. To discourage her from forming relationships with other men, he sent her letters, which he carefully wrote out in her handwriting so the police would disbelieve her. The letters stopped after he married her twelve years later, when she no longer recognised him. When Louise became attracted to Richard Carey, Bosner decided to murder her to ensure no one else could have her. On the day of the murder, Bosner, on the rooftop, lured her to the window with a mask he had used to scare her on previous nights. Once she stuck her head out to investigate, he dropped a quern on her, which he then pulled back to the roof via a rope he had tied to it. On the pretense of checking on her, he shut the bedroom window while moving the body and the rug beneath it to where they were later found. He then used Amy as part of