The Thirty-Nine Steps

" I turned on the light, but there was nobody there. Then I saw something in the corner that made my blood turn cold. Scudder was lying on his back. There was a long knife through his heart, pinning him to the floor. " Soon Richard Hannay is running for his life across the hills of Scotland. The police are chasing him for a murder he did not do, and another, more dangerous enemy is chasing him as well -the mysterious " Black Stone ".
Who are these people ? And why do they want Hannay dead ?