The Thirty Nine Steps by John Buchan ( Richard Hannay Series Book One)

Richard Hannay, the protagonist and narrator, an expatriate Scot, returns from a long stay in Southern Africa to his new home, a flat in London. One night he is buttonholed by a stranger, a well-travelled American, who claims to be in fear for his life. The man appears to know of an anarchist plot to destabilise Europe, beginning with a plan to assassinate the Greek Premier, Karolides, during his forthcoming visit to London. He reveals his name to be Franklin P. Scudder. Hannay lets Scudder...