The Three Hostages: Authorised Edition by John Buchan
After distinguished service in the First World War, Richard Hannay settles into peaceful domesticity with his wife Mary and their young son. However, news comes to him of three kidnappings. With no more than a few tantalisingly cryptic lines of verse as clues, he is soon on the trail of Dominick Medina - a charismatic polymath but a man 'utterly and consumedly wicked'.
As Hannay uncovers an international plot to twist innocent minds through hypnotism and blackmail, it appears that he has met his match in one of Buchan's most memorable villains.