The Thirty-Nine Steps is an adventure novel by the Scottish author John Buchan. It first appeared as a serial in Blackwood's Magazine in August and September 1915 before being published in book form in October that year by William Blackwood and Sons, Edinburgh. It is the first of the five novels featuring Richard Hannay, an all-action hero with a stiff upper lip and a miraculous knack for getting himself out of sticky situations. The novel formed the basis for a number of successful adaptations, including several film versions and a long-running stage play. In 2003, the book was listed on the BBC's The Big Read poll of the UK's "best-loved novels."

In May of 1914, war looms in Europe. Richard Hannay returns home to London after living in Rhodesia. One night his neighbor, an American who claims to be in fear for his life, visits Hannay. The man appears to know of an anarchist plot to destabilize Europe, beginning with a plan to assassinate the Greek Premier, Constantine Karolides, during his forthcoming visit to London.