Poirot is introduced aboard the Taurus Express in Syria, returning from solving a case in Aleppo.

Poirot meets M. Bouc at the Tokatlian Hotel, and both men take note of the sinister-looking Mr. Ratchett at dinner.

Mr. Ratchett approaches Poirot and asks him to investigate threatening letters he has been receiving.

Poirot refuses Ratchett's offer, telling him bluntly: 'I do not like your face.'

Poirot is awakened during the night by a groan from Ratchett's neighboring compartment.

The Orient Express is found stranded in snow the next morning, with Ratchett discovered stabbed to death in his compartment.

M. Bouc asks Poirot to take the murder case, and Poirot agrees to investigate.

Poirot and Dr. Constantine examine Ratchett's body, counting 12 stab wounds and suspecting several clues are deliberately planted.

Poirot decodes a burned paper scrap recovered from Ratchett's room with the words 'member little Daisy Armstrong.'

Poirot concludes that Mr. Ratchett is actually Cassetti, the gangster who kidnapped and murdered three-year-old Daisy Armstrong.

Poirot explains to Bouc and Dr. Constantine how four people died in the aftermath of Cassetti's original crime.

Mrs. Hubbard bursts into the dining car and presents a bloody knife she found hidden inside one of her bags.

The scarlet kimono that Poirot spotted during the night is found planted on top of Poirot's own luggage.

Poirot gathers all 12 suspects in the restaurant car and presents two competing theories of the murder.

Mrs. Hubbard unmasks herself as actress Linda Arden, confirms the conspiracy, and Poirot agrees to give police the false theory.

Hercule Poirot boards a train bound for Europe and encounters the unpleasant Mr. Ratchett, who asks Poirot to protect him from death threats and is flatly refused. That same night, Ratchett is stabbed to death in his locked compartment while the train becomes trapped in a snowstorm, forcing Poirot to investigate from within the confined world of the train. Poirot's examination of the body and a decoded burned note reveal that the victim was actually Cassetti, a gangster who murdered a child and escaped legal punishment. Poirot learns how the Armstrong family tragedy unfolded, with four people dying in the wake of Cassetti's crime. Through meticulous investigation, Poirot gathers key physical evidence—including a bloody knife and a planted kimono—before assembling all 12 suspects in the restaurant car. Poirot presents his true theory that all 12 passengers conspired as an act of vengeance, which Linda Arden confirms, and Poirot chooses to protect the guilty by offering police a false account.

The headline events driving the Orient Express murder investigation.

Bouc remarks to Poirot on the unusually romantic diversity of nationalities sharing the Orient Express during lunch.

Mrs. Hubbard confides to Poirot that she is frightened of her neighbor Mr. Ratchett.

Poirot opens his compartment door at night and spots a woman in a scarlet kimono retreating down the corridor.

Poirot interviews conductor Pierre Michel, who confirms he also saw the woman in the red kimono that night.

Poirot interviews MacQueen a second time, and MacQueen mentions seeing an unidentified conductor pass while he talked with Arbuthnot.

Poirot interviews valet Masterman, who admits disliking Americans and claims a toothache kept him awake the entire night.

Poirot interviews Mrs. Hubbard, who presents a metal conductor's button she discovered inside her compartment.

Poirot interviews Greta Ohlsson, who confirms she checked and found the connecting door to Ratchett's compartment properly bolted.

All three train conductors are summoned and confirm that none of them has lost a button from their uniform.

Poirot interviews Colonel Arbuthnot, who firmly defends Mary Debenham's innocence and confirms talking with MacQueen late into the night.

Poirot interviews Hardman, who reveals he is a private detective hired by Ratchett and describes a feared enemy with a womanish voice.

Poirot interviews Hildegarde Schmidt, who reports seeing an unfamiliar conductor with a womanish voice near the compartments that night.

Searching passengers' luggage, Poirot finds a Wagon Lit conductor's uniform hidden inside Hildegarde Schmidt's suitcase.

Poirot reveals the Armstrong-linked identities of Foscarelli as the chauffeur, Ohlsson as the nurse, and Masterman as Armstrong's former valet.

Poirot, Bouc, and Dr. Constantine jointly agree to present the false outside-killer theory to police, protecting all 12 conspirators.

As the Orient Express carries its diverse mix of passengers, Poirot conducts a series of interviews with each person aboard, probing their movements and relationships on the night of the murder. Witnesses including the conductor, Ratchett's secretary, his valet, Mrs. Hubbard, the Swedish nurse, and Princess Dragomiroff all offer accounts laden with partial truths and deliberate misdirection. A conductor's button, a missing uniform, and a womanish-voiced impersonator emerge as apparent clues, each carefully planted to mislead the investigation. Poirot methodically searches the passengers' luggage, uncovering the hidden Wagon Lit uniform and beginning to see the shape of a coordinated conspiracy. As the interrogations proceed, Poirot peels back the false identities of several passengers, revealing their ties to the Armstrong household staff. Ultimately Poirot and his companions choose to shield all 12 conspirators by agreeing to present a fabricated theory to the authorities.

The witness interviews and physical clues that built Poirot's case.

Poirot overhears Mary Debenham tell Colonel Arbuthnot 'Not now—when it's all over, when it's behind us' on the Taurus Express.

Poirot and M. Bouc board the Orient Express together, beginning a three-day journey across Europe.

Mrs. Hubbard rings for the conductor during the night, insisting a man had been hiding inside her compartment.

Bouc points out that Ratchett's open window is a false clue because no footprints appear in the snow outside.

Poirot notes the handkerchief and pipe cleaner in Ratchett's room appear placed too conveniently, exactly as in detective fiction.

Princess Dragomiroff reveals to Poirot that Sonia Armstrong, Daisy's mother, was her goddaughter and close personal friend.

Princess Dragomiroff declares that Cassetti's murder is, in her view, 'an entirely admirable happening.'

Colonel Arbuthnot states Cassetti deserved death while simultaneously championing trial by jury as the only sound system of justice.

Poirot rules out Colonel Arbuthnot as the killer on psychological grounds alone, despite a pipe cleaner physically pointing to him.

Poirot deduces that a grease spot on Countess Andrenyi's passport conceals a letter, suggesting her identity has been falsified.

Countess Andrenyi confesses she is really Helena Goldenberg, the younger daughter of actress Linda Arden and Daisy Armstrong's aunt.

Princess Dragomiroff reveals the 'H' handkerchief found in Ratchett's room is actually hers, with 'N' for Natalia written in Cyrillic.

Mary Debenham admits she was the Armstrongs' governess and had lied about never having lived in America.

Poirot reveals that each of the 12 conspirators stabbed Cassetti once, acting collectively as a twelve-person jury.

Linda Arden offers to accept sole blame for the murder and asks that the other eleven conspirators be spared.

From the very first moments of the journey, subtle clues signal that the passengers of the Orient Express are hiding something, beginning with a cryptic conversation Poirot overhears between Mary Debenham and Colonel Arbuthnot. As the investigation unfolds, Poirot repeatedly encounters planted evidence and deliberate lies designed to deceive him, from the convenient placement of the handkerchief and pipe cleaner to Bouc's identification of the false open-window clue. Several turning points hinge on passengers who reveal more than they intend—Princess Dragomiroff's admiration for the murder, Arbuthnot's contradictory views on justice, and a grease spot on a forged passport all shift Poirot's understanding of the case. One by one, the true identities of key conspirators are forced into the open, including Countess Andrenyi as Helena Goldenberg, Princess Dragomiroff as the handkerchief's true owner, and Mary Debenham as the Armstrong family governess. Poirot's final revelation—that the 12 passengers acted collectively as a jury—reframes the entire crime as a calculated act of moral justice. Linda Arden's offer to sacrifice herself for the others crystallizes the novel's central question about loyalty, justice, and retribution.