Frank L. Packard 
The Four Stragglers [PDF ebook] 

In the beginning we meet four Allied soldiers, who found themselves lost behind the enemy lines. When story moves on, three of them are running high-class criminal organization running scams in England and France. They stumble upon the great opportunity to make a big score in one action, and it leads to a complex and thrilling journey to the USA.
Written in 1923, well before the stock market crash of 1929, this novel is somewhat predictive of that market crash. The mystery is well conceived and the novel well written.