Clubfoot the Avenger

The Valentine William's spy thrillers are set in the period between World War I and II, when you might assume things were quiet. But the action is nonstop and all are good reads. This novel consists of three independent spy thriller novelettes strung together in a sequence: The Clue of the Purple Cabriolet, The Affair of the Constantinople Courier, and The Girl at the Hexagon. (Goodreads)