The mystery of the blue train

The Mystery of the Blue Train is a work of detective fiction by British writer Agatha Christie, first published in the United Kingdom by William Collins & Sons on 29 March 1928 and in the United States by Dodd, Mead and Company later in the same year. The book features her detective Hercule Poirot.

The novel features the murder of an American heiress, taking place on Le Train Bleu. The novel introduces the fictional village of St. Mary Mead.

Poirot boards Le Train Bleu, bound for the French Riviera. So does Katherine Grey, who is having her first winter out of England, after recently receiving a relatively large inheritance. On board the train Grey meets Ruth Kettering, an American heiress leaving her unhappy marriage to meet her lover. The next morning, though, Ruth is found dead in her compartment, a victim of strangulation. The famous ruby, "Heart of Fire", which had recently been given to Ruth by her father, is discovered to be missing. Ruth's father, the American millionaire Rufus Van Aldin, and his secretary, Major Knighton, persuade Poirot to take on the case. Ruth's maid, Ada Mason, says that she saw a man in Ruth's compartment but could not see who he was. The police suspect that Ruth's lover, the Comte de la Roche, killed her and stole the ruby, but Poirot does not think that the Comte is guilty. He is suspicious of Ruth's husband, Derek Kettering, who was on the same train but claims not to have seen Ruth. Katherine says that she saw Derek enter Ruth's compartment. Further suspicion is thrown on Derek when a cigarette case with the letter "K" is found there.