Double Sin is a short story by Agatha Christie which was first published in the Sunday Despatch in September 1928 and in Detective Story Magazine in the U.S. in March 1929 (as "By Road or Rail"). In the U.S., the story was gathered and included in the collection Double Sin and Other Stories, published by Dodd, Mead and Company in the U.S. in 1961. In the U.K., the story was not anthologized until it was included in Poirot's Early Cases in 1974.