The Mystery of the Blue Train is a work of detective fiction by Agatha Christie and first published in the UK by William Collins & Sons on March 29, 1928 and in the US by Dodd, Mead and Company later in the same year. The UK edition retailed at seven shillings and sixpence (7/6) and the US edition at $2.00. The book features her detective Hercule Poirot.
Poirot boards Le Train Bleu, bound for the French Riviera. So does Katherine Grey, who is having her first winter out of England, after having inherited a huge sum. While on board she meets Ruth Kettering, an American heiress bailing out from a 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, convince Poirot to take on the case. Ruth's maid, Ada Mason, says 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 rubies, but Poirot does not think he is guilty. He