The Continental Op gets hired by a blowhard businessman with a trigger temper and a legacy of shoddy merchandise sold to the US for World War I. Seems that someone has kidnapped his headstrong daughter, his only living relative, and demanded money to make amends for all the soldiers he let die in France...
Now, if you've read or seen at least two other stories involving kidnapping, you'll know how this story ends: the Op tracks down the kidnapper, who turns out to be the headstrong daughter who just wants to start life over away from dear old dad. It really doesn't matter what kidnapping stories you read; just about any story will give you the detective genre chops to identify the kidnapper.
I'm not entirely sure what this story would look like to the 1920s reading audience, for whom Hammett was an unfamiliar name. (This was his first story published under his own name.) Maybe it was a shock?
Still, even if the mystery (what happened?) isn't very mysterious, there's several pleasures here, such as they mystery of how: how will the Continental Op solve the crime? There's a lot of attention paid to the Continental Op's shoe-leather detection--shadowing the ransom-payer, asking around at various stores, recognizing the minor con-man helping the daughter's scheme.
There's also the pleasure of the Op's ironic detachment as he observes all this. So his first view of the businessman's world:
Harvey Gatewood had issued orders that I was to be admitted as soon as I arrived, so it only took me a little less than ﬁfteen minutes to thread my way past the doorkeepers, ofﬁce boys, and secretaries who ﬁlled up most of the space between the Gatewood Lumber Corporation’s front door and the president’s private ofﬁce.This looks like just a cute note about a man whose corporate life has taken over his personal life, but it turns out to be a clue that the Op uses to identify the kidnapper. We could also see this as one of Hammett's signature moves, filling up the world with lots of spear carriers and incidentals, any of whom might turn out to be important to the mystery. There's a lesson there for budding crime writers: you can bury clues in snark.