The chief difficulty seems to be the identity of the murdered man. Fleeing from a past in America, Mr. Rachett obviously had enemies. Inspecting his berth, Poirot finds many pieces of evidence - almost too much evidence. Among them, a burned piece of paper on which Poirot discerns a name: Daisy Armstrong. The dead man is discovered to be none other than Casseti, the notorious kidnapper, who fled the country after his money successfully saved him from the charge of kidnapping and killing Daisy Armstrong, a three year old child. Is someone related to the Armstrongs on the train? Poirot hunts through the passenger list and interrogates everyone, but can find no connection. Everybody has an alibi, no one seems implicated, and yet.......things seem to be too neatly worked out.
In the end, it is the first clue that helps Poirot solve the case: the overcrowded Calais coach. The evidence itself is a hopeless tangle leading him first to one suspect, then another. Poirot, more than ever before, must rely solely on his 'grey cells' and solve the murder before the snowdrift is cleared. Mr. Bouc, the director of the line, appeals to Poirot thus,
Interview the passengers on the train, view the body, examine what clues there are and then - well, I have faith in you! I am assured that it is no idle boast of yours. Lie back and think - use (as I have heard you say so often) the little grey cells of the mind - and you will know!
Atmosphere. That's what you feel when you open Murder on the Orient Express. The whole book is steeped in it. So much so, that you forget to follow the facts. Who is the murderer is a faint question in the background and you yourself are intoxicated by all the trimmings: the setting, the characters, the elusive pieces of evidence. It's so much fun to read this book. One of my top Agatha Christie recommendations.
How many times has Hercule Poirot said that he does not approve of murder? Well, in this case you'll see him tested. It is one of the cases that never fails to move me. Whatever your position on revenge may be, Murder on the Orient Express just might change it.