I was a little disappointed while reading the book because I reached to the right conclusion at the very beginning of the story based only on three pieces of information:

1) The train was unusually packed. “It is incredible, Monsieur. All the world elects to travel tonight!” And the author told us some possibilities through M. Bouc, “Ah, without doubt there is some party of journalists–of politicians–?” This told us that it was not a coincidence that all the travelers gathered on the train.

2) Multiple people stabbed the body. Some blows were struck with the left hand, while the others obviously right-handed. Some blows were struck in such a great force that they must be delivered by men, while others were so light and likely by feeble women. This matches the fact that there were all kinds of travelers on the train at the same time.

3) The Armstrong kidnapping case. It was such a tragedy, especially when the guy behind all the abhorrer was escaped by bribing. This gave a good reason that many people wanted him to die.

Based on these three reasons, it was not so difficult to guess that several, if not all, of the travelers are involved in the murder.

I guess this is a common issue while reading the classic mystery thrillers. These stories are so well-known and their plots are wildly borrowed by many other books and movies. So I often have the feeling that these classic stories are “familiar”.