Stephen Norton's murder is the decisive reversal in the novel’s final mystery: what first appears to be a locked-room suicide is revealed in Poirot’s posthumous explanation as a killing he planned and carried out. The murder turns Poirot’s opposition to Norton’s manipulation into an act of lethal judgment, while making the investigation’s apparent solution part of the deception.

Background and Motive

Norton had previously manipulated other people by planting suggestions and exploiting the suspicions they produced. After Barbara Franklin’s death was ruled a suicide, he was dissatisfied: the verdict had denied him the extended drama of suspicion, fear, and legal pursuit that he sought. He therefore began hinting that he had witnessed a compromising encounter involving Judith and Dr Franklin, an insinuation that could cast doubt on the suicide verdict and expose the pair to renewed suspicion.

Poirot understood the danger in Norton’s proposed story. By suggesting that he had seen Dr Franklin with Judith, Norton could redirect attention toward a possible motive for Barbara Franklin’s death, even though his earlier hint had suggested Major Allerton. Poirot decided that he had to act before Norton could set this new accusation in motion. He arranged for Hastings to bring Norton to his room that night and confronted him with what he knew.

The Killing

Norton did not deny Poirot’s accusation. Instead, he smirked and treated Poirot’s proposed response as an amusing choice between a dagger and a cup of poison. Poirot chose the latter: while they were about to have chocolate, he handed Norton the cup he had just poured. Norton asked to drink from Poirot’s cup rather than his own, but Poirot agreed because both cups contained the same drug. Poirot says Norton’s portion put him to sleep, while his own had little effect because he had developed tolerance to his regular sleeping tablets and counteracted the dose with strychnine tonic.

Once Norton was asleep, Poirot put him into his wheelchair and wheeled him behind the curtains in the window recess. Curtiss later put Poirot to bed. When the house was quiet, Poirot moved Norton to his room, using his knowledge of the wheelchair’s mechanisms to carry out the transfer. He then used Hastings as an unwitting witness in the construction of the apparent suicide.

Staging the Locked Room

Poirot explains that he wore a wig and false moustache, and that he had obtained a replica of the wig after pretending to burn the earlier one accidentally. Disguised in Norton’s dressing gown, with his grey hair ruffled, he came down the passage and knocked on Hastings’s door. Hastings saw what appeared to be Norton leave the bathroom and limp into his room; he also heard the key turn in the lock from the inside. The scene gave Hastings a seemingly direct observation of Norton entering a room that then appeared to be secured from within.

After Hastings had seen the disguised figure, Poirot restored the dressing gown to Norton, laid him on the bed, and shot him with a small pistol he had kept locked away. He had previously placed that pistol conspicuously on Norton’s dressing table on two occasions when Norton was absent, so that the housemaid could later say she had seen it there. Poirot then put the key in Norton’s pocket, locked the door from the outside with a duplicate key he had possessed for some time, and wheeled the chair back to his room. The key, the apparent inside lock, Hastings’s mistaken identification, and the pistol together made the scene look like suicide.

Discovery and False Verdict

The room was broken open, and Norton was found on his bed in his dressing gown, with the key in his pocket and the pistol in his hand. A small hole in the centre of his forehead was visible. When Hastings asked whether Poirot believed Norton had shot himself, Poirot answered that Norton had been deliberately killed. His refusal to accept suicide stood against the apparent coherence of the room and the evidence arranged within it.

Nevertheless, the inquest returned a verdict of suicide. The door had appeared locked from the inside, its key was in the dead man’s pocket, the windows were shuttered, and the pistol seemed to be Norton’s; the housemaid had previously seen it on his dressing table. The surgeon noted that a self-inflicted shot precisely in the centre of the forehead was unusual, but that remained the sole stated doubt. Headaches and failing investments were offered as possible reasons for suicide, though the account acknowledges that they were hardly compelling. The scene was accepted as a beautifully staged crime without an alternative solution, and Hastings concluded that Norton had won his duel with Poirot.

Revelation and Significance

Poirot’s written explanation reinterprets the evidence after his death. The apparent witness who saw Norton enter the locked room was Poirot in disguise; the locked-room conditions were produced by the duplicate key; and the pistol had been planted in plain sight beforehand to support the suicide account. Hastings’s observation was not fabricated, but carefully made to mislead him about whom he had seen. The staged scene thus converted a trusted witness and ordinary physical clues into instruments of concealment.

The murder also reverses the roles of investigator and killer. Poirot had confronted Norton, declared his intention, and knowingly administered the drug; he then used the conventions of the suicide investigation to hide what he had done. Norton’s own taste for engineered suspicion prompted Poirot’s intervention, but the result was not a lawful resolution: the official verdict remained false, and the truth reached Hastings only through Poirot’s final account. The event closes the duel not with public vindication, but with a confession that exposes both the ingenuity of the deception and the moral cost of stopping Norton by killing him.