The Honour of Israel Gow by G.K.Chesterton

Father Brown and Flambeau, now a private detective, arrive at Glengyle Castle in Scotland to help Inspector Craven of Scotland Yard solve the strange death and secretive burial of the late earl, a secluded man who lived as a hermit with his servant, the silent Israel Gow. The Earl died and was buried in secrecy by Gow. The clues to the crime, if there has been a crime, are large in number and baffling. What is behind these odd and mysterious events?