The Thirty-Nine Steps by John Buchan

Richard Hannay has just returned to England after years in South Africa and is thoroughly bored with his life in London. But then a murder is committed in his flat, just days after a chance encounter with an American who had told him about an assassination plot which could have dire international consequences. An obvious suspect for the police and an easy target for the killers, Hannay goes on the run in his native Scotland where he will need all his courage and ingenuity to stay one step ahead of his pursuers.