Have You Got Everything You Want? — Agatha Christie

Elsie Jeffries, married for eighteen months to successful businessman Edward Jeffries, meets Parker Pyne by chance on the Simplon-Orient Express. She has seen Pyne's advertisements and feels he may be able to help her. She tells Pyne she has seen a fragment of a letter left on Edward's blotting pad, which points to some sort of plot against her, to be carried out while she is on the train to Stamboul...