The Spotted Handkerchief
Written by
William Le Queux
Copyright 1921
Likely published in The Royal Magazine, October 1920. 2nd story in the collection .
Word has leaked to British Intelligence that a collusion between Greece and Germany to find a way to reduce Germany's required War Reparation payments. Claud Heathwaite is sent Spain where the plot is taking place to learn the facts. It nearly costs him his life.