Ms. Allingham creates a mystery with a very large cast of unusual characters. It wasn't until I finished the book that I realized "the smoke" in the title is London. Or at least I think it is. They used to call London the "Big Smoke" due to the pollution from the coal house fires.
It has an interesting mystery among pages of unnecessary details. I got lost several times, but just sticking to the main story is a good read. It's about a buried treasure that a soldier leaves to his wife during the war ... in case he doesn't survive the war, the instructions will be sent to her future husband. When he checks on the treasure's safety during the war, he shares the details with his buddies ... who greedily spend the next five years trying to find the treasure and prevent the widow from remarrying.