Murder on the Orient Express by Agatha Christie

Agatha Christie (Wikipedia) was one of the most prolific writers in the detective genre and created two most unlikely characters in the form of detectives. Till then, the character of Sir Arthur Conan Doyle's Sherlock Holmes defined the character of the detective - a man who is exceedingly smart and knows it, but is not very vain, and who can be urged to great action when he needs to, also a man of great physical strength (even if his frame does not suggest it). Both the characters created by Agatha Christie were very different, with Miss Marple being a frail old lady, but with a terrific mind and ability to think through things (most of which occur in her village) even when she is engrossed in daily routine manners, and then the other character who is the central character of this novel, the egg shaped Belgian detective Hercule Poirot.
A vain man, who knows that he is very smart, and is not above telling other people about this. He is obsessed with things being proper, making sure that his mustache is well maintained and becomes uncomfortable when he finds out that people do not know about him. At the same time, he is very capable, like Sherlock Holmes, of putting facts together, and of being able to find the discrepancies that help him crack the crime. Hercule Poirot was introduced by Agatha Christie in 1920 in 'The Mysterious Affair at Styles' and appeared in 33 of Christie's novels and 54 short stories.



The story has a twist in the end, when Hercule Poirot actually presents 2 different options as to who did the murder, and presents it in such a way that the decision will eventually go only one way. The novel is set on the Orient Express, near Belgrade. Poirot is returning from a case in Syria, and gets a berth on the Orient Express with difficult, due to the help of his friend Monsieur Bouc, a director of the company which operates the Express. He meets a number of people on the train (and is very surprised at the fact that it is full, something very unlikely at this time of the year). He also meets a man who exudes violence, Mr. Ratchett, who asks him to act as his defender from people out to get him and Poirot refuses.
On the second night, he hears a noise in the night from the neighboring compartment, occupied by Mr. Ratchett. After some time, the conductor is called by Mrs. Hubbard who is terrified that somebody is in her coach. There is some further commotion, but then he sleeps. When he gets back, he is notified that the train will not move further since it is stuck in a snowdrift, and also learns that Mr. Ratchett has been murdered during the night, struck multiple times with a knife; and Poirot is the one called on for help.
After some investigation, Poirot discovers that Mr. Ratchett was actually a leader of a criminal gang and his real name was Cassetti. He was the chief leader of the plot to abduct the rich heiress Daisy Armstrong, and she was then murdered inspite of the ransom having been paid by her parents. Both her parents died subsequently, her mother in grief which induced an early childbirth and she died, her father shooting himself. It also caused suspicion in other house members such as the maid who was suspected and who killed herself because of this suspicion.
Poirot finds that the clues and events of the night are set in such a manner that every person has an alibi, sometimes from unexpected resources; and eventually starts to think in a holistic sense, trying out a theory that the other members of the investigating party (the official and the doctor) are unable to think through. Finally, through some conjecture (and this was the weak link in the book - everything seemed to settle through easily), he is able to deduce the actual facts and the names of the murderer(s). He then presents this theory, as well as an alternative theory to the other members of the team, and asks them to pick the one that they prefer. What choice do they make of the theory to present to the Yugoslav police when they will reach there ?