Mr. Standfast

Mr Standfast is the third of five Richard Hannay novels by John Buchan, first published in 1919 by Hodder & Stoughton, London.
It is one of two Hannay novels set during the First World War, the other being Greenmantle (1916); Hannay's first and best-known adventure, The Thirty-Nine Steps (1915), is set in the period immediately before the war started.
The title refers to a character in John Bunyan's Pilgrim's Progress, to which there are many other references in the novel; Hannay uses a copy of Pilgrim's Progress to decipher coded messages from his contacts, and letters from his friend Peter Pienaar.
Set in the later years of World War I, Brigadier-General Hannay is recalled from active service on the Western Front to undertake a secret mission hunting for a dangerous German agent at large in Britain.