Published in 1934, Agatha Christie’s Murder on the Orient Express is a classic example of the locked room mystery—a trope of suspense fiction in which a crime is committed under seemingly impossible conditions. Here, as in all of Christie’s novels, the crime is murder, the victim an unknown passenger named Mr. Ratchett, stabbed twelve times, and the scene of the crime the claustrophobic sleeping berths of the Orient Express.

Fortunately, or unfortunately as the case may be, one of the passengers happens to be Hercule Poirot, the Belgian detective bestowed with astounding intellect and even more astounding mustaches. Even more fortunately, the train has been caught in a snowstorm and will be unable to continue to its destination for some time. The murderer is effectively trapped. Poirot quickly sets his “little gray cells” to work and begins the investigation, which includes extensive interviews of the other passengers. These passengers are a strange mix of nationalities and social standing: a Russian princess, a Hungarian count and countess, a missionary from Sweden, businessmen from Italy and America, an American tourist, a British Colonel and a British valet, as well as a secretary, a governess, a German maid, and the French train conductor. They seem to have no connection, either with each other or the murdered man. But Poirot does not jump to conclusions. He quickly discovers Mr. Ratchett’s true identity and hypothesizes that at least one person on the train may have had good reason to want him dead.

The clues are as eclectic as the passengers and include a red kimono, a burned letter, a pipe cleaner, and a monogrammed handkerchief. Some of these are red herrings, false clues, which the murderer uses to lead Poirot astray. Of course, the Belgian detective discovers the culprit and, in classic style, gathers all the suspects together to reveal the murderer’s identity.

One of Christie’s most popular novels, Murder on the Orient Express referenced a real-life mystery: the kidnapping and murder of Charles Lindbergh’s child in 1932. As a testament to its continued popularity, the story has been adapted into a movie, television miniseries, comic book, and video game. Unfortunately, the real Orient Express did not share the same popularity; in 2009 the train route stopped operation.

Hercule Poirot finds himself the uninvited guest at the scene of an elaborately planned murder on wheels. The Belgian detective is making his way from Istanbul, Turkey, to London, and he is looking forward to a leisurely trip and a chance to clear his head, a chance to rest his “little grey cells,” as Poirot refers to his brain.

A good friend of Poirot, M. Bouc, is an administrator with Wagon Lit, the train company that operates the Orient Express. Poirot prefers to travel first class. Because it is winter, off season for tourists, the detective is assured by Bouc that finding a first-class cabin on the train will be easy. To their surprise, the car leaving Istanbul, the Calais Coach, is nearly full. There is, however, one no-show, and Poirot finds himself sharing a compartment with Hector MacQueen, the private secretary to a wealthy American, Mr. Ratchett.

Poirot is introduced by Bouc to Dr. Constantine, a Greek physician, traveling in the next car. On the first night of the journey, as they sit in the dining car, Bouc points out to Poirot the variety of travelers in the dining car: the rich and the poor. Some are English, some American, some French, some Italian, some Russian, some Hungarian—an array of passengers from differing socioeconomic backgrounds and different cultures. Where else in the world, Bouc wonders aloud, could one find such an assortment of people beneath one roof? Yes, Poirot thinks to himself, perhaps only in America.

The first night passes peacefully, and Bouc moves Poirot from his shared cabin with MacQueen to a private one next door to Ratchett. During the second night of the trip, Poirot has trouble sleeping, awakened by voices, service bells summoning conductor Pierre Michel, and thumping on his cabin door. At about 1:15 a.m., Poirot sticks his head out of his cabin and sees a woman wearing a kimono with a dragon print walking down the corridor. He hears his neighbor, Ratchett, tell the conductor in perfect French that nothing is wrong and that he had not meant to ring his service bell. The train is stopped, too, as an avalanche of snow covers the tracks.

Ratchett, Poirot has determined, is an evil man. The evil shows on his face, and Poirot has taken an instant dislike in him. Earlier in the evening, Poirot had been approached by Ratchett and was offered a job—to keep Ratchett alive. Ratchett has been receiving hate mail and otherwise threatening letters. Poirot turns down the offer of employment.

The next day, Ratchett is discovered dead in his cabin, and there are many clues. A pipe cleaner belonging to the Englishman, Colonel Arbuthnot, is found on the floor of the murdered man’s compartment. An expensive lady’s handkerchief, belonging to Princess Dragomiroff, also is found on the floor. The dead man’s watch is in the pocket of his pajamas, broken and stopped at 1:15 a.m. The window of the cabin is open. A button from a conductor’s uniform is found near the bed of Mrs. Hubbard, Ratchett’s American neighbor in the connecting cabin, who had complained of a man lurking in her room during the night.

For Poirot, there are too many clues. Too many clues at a crime scene means tampering, Poirot thinks. How does one separate the real clues from the planted ones? One of the best clues, one that Poirot thinks is real, is a piece of burned paper in an ashtray. The tray has two different types of matches in it. One type of match had also been found in the cabin of the dead man; the other type of match had not. Using wire mesh from a woman’s hatbox, Poirot carefully places the burned paper between two layers of wire mesh and lights a match beneath it to reveal the words once written on the paper. These few words on the burned piece of paper become the best clue, leading Poirot to the dead man’s true identity. Ratchett is, in reality, a killer and kidnapper of children. His real name is Cassetti.

Cassetti had been arrested and acquitted in the infamous Daisy Armstrong kidnapping and murder case in the United States. The kidnapping and murder of Daisy Armstrong destroyed her entire family; her father and mother, an unborn child, and her nursery maid all died as a consequence of this hideous action.

As Poirot inspects the body of the dead man, he thinks Cassetti has finally received justice, if not strictly via the letter of the law. The corpse has twelve dagger wounds, the range in severity of puncture wounds suggesting some made by a right-handed killer, others made by a left-handed killer. Some wounds are deep, while others only break the skin’s surface. After interviewing each passenger in the Calais Coach and after examining everyone’s luggage, Poirot learns several facts that seem unimportant and unrelated. For example, there is a spot of grease on Countess Andrenyi’s passport, partially obscuring her first name. A conductor’s uniform with a missing button is found in the luggage of Greta Ohlsson, a Swedish nurse. Even more interesting, the kimono with the dragon print is found in Poirot’s own luggage.

In the dining car of the Calais Coach aboard the Orient Express, Detective Poirot identifies the killer, but only after he details the evidence and slowly puts the proverbial noose around the neck of the guilty. The kicker, the surprise, is that everyone is guilty: They all did it.

Poirot has been an audience of one surrounded by a cast of twelve killers, each suspect playing a role, acting out his or her part, trying to mislead the detective. From Poirot’s vantage point, he is challenged to match his wits against the collected intelligence of a dozen minds bent on revenge.

Poirot, in the end, reveals two truths: what really happened and the agreed-upon truth that Poirot offers to the killers. Poirot, during his big reveal, presents both possibilities to his cast of suspects; the second possibility is deemed fairer and more just and so becomes the official truth. Cassetti, the murdered killer, had received an alternative form of justice at the hands of those he had victimized by his actions. Although he had been intent on solving the crime aboard the Orient Express, Poirot, now, is not as intent on seeing the guilty punished.

Agatha Christie's seminal mystery novel Murder on the Orient Express was first published as a complete work in 1934. The material originally appeared as a serial in the Saturday Evening Post from July through September of 1933.

The novel's main character, Hercule Poirot, is a Belgian private detective called to London to solve a case. He boards a train, the titular Orient Express, and secures a sleeping car through the help of his friend M. Bouc. While on the train, Poirot meets a passenger named Ratchett who asks for Poirot’s help: Ratchett believes his own life is in danger. Poirot later discovers that Rachett has in fact been murdered on the Orient.

Poirot visits Ratchett’s sleeping car and finds a clue, a burned piece of paper with the word “Armstrong” written on it. Poirot thinks the paper may link Ratchett's murder to another crime that happened many years ago in the United States. That case involved a man named Cassetti. It is believed that Cassetti kidnapped and murdered a baby, which led to the murder of the baby’s father, mother, and nursery maid. The killings are collectively referred to as the "Armstrong Case."

Poirot deduces that Ratchett was really Cassetti. After Poirot finds a pipe cleaner and a button from a conductor’s uniform, Poirot begins to suspect Colonel Arbuthnot and Pierre Michel as the murderers of Rachett. He interviews thirteen main suspects and traces the hidden links among the passengers. As the novel progresses, Poirot reveals the true identities of several characters. He ultimately proposes two possible solutions for the Ratchett murder.

Agatha Christie was one of the most innovative, best-selling writers of detective fiction, and her Murder on the Orient Express remains a classic of the genre. Readers enjoy its quick pace as well as the motives and actions of the characters. In 1974, the novel was made into a successful movie directed by Sidney Lumet and starring Albert Finney, Lauren Bacall, Ingrid Bergman, and Sean Connery.