Poirot applauds Hastings’ insight about Conneau and urges him to continue. Hastings proposes that Conneau drifted to Merlinville, murdered Renauld out of jealousy over Madame Daubreuil, tried to blackmail her, and then died of an epileptic fit. He suggests that Jack, arriving afterward, agreed with Madame Daubreuil to cover the man’s death up to protect Marthe. Poirot reminds him that Conneau couldn’t have blackmailed Madame Daubreuil since she could have revealed him as a wanted murderer.

Poirot then constructs his own account, identifying Madame Daubreuil as Madame Beroldy from the earlier murder case. The identical fabricated story of foreign intruders in both cases points to a single author, Conneau himself. Poirot proposes that Conneau worked with Mrs. Renauld as his accomplice. He walks Hastings through a timeline of the past few weeks, highlighting Renauld’s changed behavior in Merlinville, his blackmail payments to Madame Daubreuil, his quarrel with Jack over Marthe, the revisions to his will, and the events of June 7, when the unhoused man died.

Poirot reminds Hastings that Renauld’s body wore a notably long overcoat while Jack’s was short. He deduces that Jack left for Paris hurriedly and in anger, grabbing his father’s coat by mistake. This means the love letter found in the pocket was written to Jack, not his father.

Poirot places the unhoused man’s death on the morning of June 7. That confrontation prompted Renauld to send for Poirot, dispatch Jack abroad, and dismiss the chauffeur. He proposes that the man’s mysterious evening visitor was a woman named Bella Duveen, Jack’s correspondent, who rejected a payment Renauld offered her.

Applying Giraud’s belief that women lie for themselves, their lovers, or their children, Poirot reasons that Mrs. Renauld was protecting none of those unless her husband was Conneau. The man she loved most was her husband. Therefore, Paul Renauld and Georges Conneau are the same person. Hastings objects that this means Renauld planned his own murder. Poirot confirms it.

Poirot clarifies that Renauld planned his disappearance, not his death. Conneau, wanted for murder, had fled to Canada, rebuilt his life under the alias of Paul Renauld, and eventually returned to France. In Merlinville, he was recognized by Madame Daubreuil, who began blackmailing him. When Jack fell in love with Marthe, Renauld faced exposure if he tried to stop the marriage, so he and Mrs. Renauld devised a plan: He would fake his death, she would manage the inheritance as a widow, and they would reunite abroad.

When the unhoused man died of an epileptic fit in their garden, they had the body they needed to substitute for Renauld’s. They dressed the corpse in Renauld’s clothing, stabbed it with the dagger, and intended to use the lead piping to make the face unrecognizable. The grave was placed where a golf bunker was to be dug, ensuring its discovery. Renauld planned to bind his wife, don the dead man’s ragged clothing, and slip away on the 12:10 train. Bella Duveen’s visit caused a dangerous delay, but he managed to see her off. Then, while digging the grave, an unknown person stabbed him from behind.

Two crimes therefore exist: The staged disappearance Renauld engineered, and the real murder committed by a still-unidentified killer. The dark hair found coiled on the dagger belonged to Mrs. Renauld, whose once-dark hair has largely turned silver, a detail that misled Giraud entirely. Arriving to identify a body she expected to be the unhoused man’s, Mrs. Renauld instead found her husband’s actual corpse, and she has been forced to maintain her false story to protect her son from scandal ever since.

Poirot decides to travel to England to locate Bella Duveen, whom he deduces must be a stage performer. He shows Hastings a photograph taken from Jack’s room, which is inscribed with the message, “With love from Bella” (173). Hastings stares at the image and recognizes the face of “Cinderella.”

Hastings conceals his recognition from Poirot. During the crossing to England, he thinks through “Cinderella’s” likely movements: She must have left the train at Calais, traveled to Merlinville that evening, and gone to the villa around the time the servants described Renauld receiving a visitor. He wonders whether she could establish an alibi for Jack, while dreading what Poirot already suspects about her.

In London, Poirot enlists Joseph Aarons, a theatrical agent, who identifies the woman in the photograph as one of the Dulcibella Kids, two sisters who perform as singers, dancers, and acrobats. The duo is recently back from Paris. The next morning, a note from Aarons informs Poirot that the Dulcibella Kids will be performing at the Palace Theatre in Coventry that evening, and Poirot and Hastings attend.

Hastings recognizes “Cinderella” among the performers but leaves early, feeling troubled. Shortly afterward, “Cinderella” appears at the hotel, having followed him from the theatre. Pale and frightened, she asks whether Poirot is the detective searching for her.

Hastings comforts her and asks gently whether she took the dagger. She says that she did because she feared there may have been fingerprints on the weapon. He then declares his love for her and reconstructs what he believes happened: Still near the villa after her meeting with Renauld, she saw a figure on the golf links wearing a coat she recognized as Jack’s and struck out in a jealous rage, accidentally killing his father. Her reaction seems to confirm the account. When Hastings assumes she still loves Jack, she contradicts him fiercely and declares she loves Hastings.

Poirot appears at the door. Hastings delays him long enough for “Cinderella” to flee, and Poirot accepts this calmly, acknowledging he’d known from the start that Hastings recognized the woman’s photograph. Hastings declares he must now work against Poirot and fabricates an alibi for her: He claims to have traveled with “Cinderella” from France on the day of the murder and parted from her at Victoria Station that evening, making her presence in Merlinville impossible. Poirot calls the invention ingenious and marvels at the power of love.

The next morning, Poirot informs Hastings that the Dulcibella Kids have cancelled their Coventry engagement and vanished. Hastings is satisfied that Bella made use of the head star he gave her but troubled because he has no way to tell her about the alibi he invented on her behalf.

Poirot announces his intention to return to France immediately. Hastings knows he must go, too, because the only way to protect Bella is to keep Poirot under observation. Poirot agrees without protest, openly preferring Hastings at his side to a clumsy attempt at surveillance. They acknowledge, almost amicably, that they are now working at cross-purposes.

A passing thought of Jack jolts Hastings. Absorbed in Bella’s situation, he’d barely considered the innocent man awaiting trial. He’s horrified to realize that, in shielding her, he may be helping to send Jack to the guillotine. He tells himself Jack will almost certainly be acquitted and resolves to trust Poirot to clear him without exposing Bella though an uneasy fear persists.

Returning to France, Poirot and Hastings visit Hautet, who reports that Jack is making no effort to defend himself and is offering only a blanket denial. He invites them to observe the next interrogation, confirms that Mrs. Renauld remains unconscious, and hands Poirot a letter that arrived in his absence.

Outside, they encounter a self-satisfied Giraud. When Poirot declares Jack innocent, Giraud dismisses him, and Poirot responds by challenging him to a wager of 500 francs on who identifies the true murderer first. They then meet Stonor, who shares their conviction that Jack didn’t commit the crime. Poirot asks him to send word the moment Mrs. Renauld regains consciousness.

At the hotel, Poirot dismantles the dagger defense Hastings had been relying upon. The detective’s research revealed that Jack commissioned three identical daggers, not two, meaning he would still have had one after giving the others to his mother and to Bella. Poirot then opens the letter, in which Marthe begs him to save Jack.

They drive at once to the Villa Marguerite. Marthe, barred from visiting Jack in prison, immediately accuses Mrs. Renauld and Stonor of committing the murder for the inheritance. Poirot asks quietly whether she knows her mother’s real name, and her tearful reaction confirms she does. Asked whether she knew who Renauld truly was, she’s genuinely baffled. Poirot walks her through the full truth of the case. When he finishes, an awestruck Marthe kneels before him and begs him to save the man she loves.