The Three Hostages

The Three Hostages is the fourth of five Richard Hannay novels by Scottish author John Buchan, first published in 1924 by Hodder & Stoughton, London.
Hannay had previously appeared in The Thirty Nine Steps (1915), his most famous adventure in which he battles German spies across England and Scotland, and two books about his activities during the First World War, Greenmantle (1916) and Mr Standfast (1919).
After the War, Hannay is married to Mary and living peacefully in the Cotswolds, when he receives a request to help solve the mysterious kidnapping of the children of three prominent people. Given nothing to go on but a few mysterious clues, Hannay, assisted by friends like Sandy Arbuthnot, must track down the dastardly villains behind the plot before it's too late...