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.
During the later years of the First World War 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. Hannay is required to work undercover disguised as a pacifist, roaming the country incognito to investigate a German spy and his agents, and then heads to the Swiss Alps to save Europe from being overwhelmed by the German army.
On November 5, 2019, the BBC News listed Mr Standfast on its list of the 100 most influential novels. (wikipedia.org)