The Mystery of the Blue Train

The writing of this book (part of which took place on the Canary Islands in early 1927) was an ordeal for Agatha Christie. The events of 1926 with the death of her mother and her husband's infidelity had left a deep psychological scar on Christie. Now separated from Archie and in need of funds, she turned back to writing. The dedication "To the two distinguished members of the O.F.D. - Carlotta and Peter" also references this difficult time. O.F.D. stood for Order of the Faithful Dogs and both Carlotta, hired by Christie as a secretary and Rosalind's governess, and Peter, Rosalind's much loved dog were in that camp as opposed to the Order of the Faithless Rats who had turned away from her.

The story itself, even though derived from the 1923 Poirot short story The Plymouth Express, did not come easily to her and she referred to this novel in her autobiography stating that she "always hated it". The critics did not agree with her. The Times Literary Supplement said, "The reader will not be disappointed when the distinguished Belgian on psychological grounds builds up inferences almost out of the air, supports them by a masterly array of negative evidence and lands his fish to the surprise of everyone".

The novel also contains a number of firsts: there is a reference to the fictional village of St. Mary Mead, which would later be the home of Agatha Christie's detective Miss Marple; the first appearance of the minor recurring character, Mr Goby, who would also appear in After the Funeral and Third Girl and the first appearance of Poirot's valet, George.

The graphic novel was first published in French in 2005 under the title Le train bleu and the story was adapted for television with David Suchet as Poirot in 2006. Reset in the late 1930s to match the rest of the Poirot TV series, the adaption by Guy Andrews was directed by Hettie Macdonald who also directed the 2013 adaptation of Curtain: Poirot's Last Case.