This is a fairly OK mystery novel. A man is murdered aboard a train bound for Paris. Only somebody in the same car could have done this, so the number of suspects is limited. French police investigates the crime, only to arrive to a completely wrong conclusion. It does not help any that some of the passenger behave in a way that would get them beaten by modern friendly cops (ah, the realities of our life).
The novel is short, just the right length for it not to get boring. For a better mystery on a train, look into [b:Murder on the Orient Express|16304|Murder on the Orient Express (Hercule Poirot, #10)|Agatha Christie|http://d.gr-assets.com/books/1309204192s/16304.jpg|2285570].