Snowbound in the Balkan Hills, the Orient Express's passengers awaken to find Mr. Ratchett stabbed twelve times. Poirot, without the aid of modern conveniences, must solve the case, because the murderer might not have left the train. Though there is an abundance of clues, are they factual or simply red herrings? Poirot must decide. When it is discovered Mr. Ratchett is really the infamous Cosetti who kidnapped and murdered the beloved Armstrong baby, the pieces start to fit together. Twelve wounds and twelve people on a jury: could it be that all twelve passengers on the train were involved in the deed? It is found each passenger's life was greatly disturbed by the Armstrong kidnapping. Poirot wonders if they were justified in killing Cosetti so he proposes two solutions: one, that the murderer escaped from the train; and two, that they all conspired to kill Cosetti for vengeance of the death of sweet Daisy Armstrong. The manager of the train decides to tell the authorities Poirot's first solution because Cosetti was a fugitive and he did deserve punishment.

Agatha Christie's unique style is captivating. She gives her protagonist, Poirot, a definite personality without dwelling on his life story. Poirot is a little vain, proud of his moustache, and, as specifically shown in this book, sympathetic. Though Christie's Poirot bears some resemblance to Sherlock Holmes, her conclusion to the book is much less of an enigma to the reader. She presents all the evidence clearly and Poirot voices his thoughts to keep the reader informed. Murder on the Orient Express has all the elements of a suspenseful mystery.