The Shadow is as efficient as usual, but bad luck stalks him. He tails a couple of guys who are in turn tailing Bron. But these turn out to be good guys--ex-smugglers (tough guys now apparently working on the right side of the law) that Bron has hired as bodyguards. When the Shadow tries to quietly leave the scene in the guise of Lamont Cranston, he's knocked out and kidnapped by guys who really were after Bron.
Fortunately, the Shadow's agents are smart and able to improvise. A chance to shine is always fun to see in any Shadow story,so when Harry Vincent helps his boss getaway by impersonating the Shadow himself, it's pretty darn cool.
The action soon moves to the coast of Maine, in a remote area that includes an 18th Century fort originally built to battle pirates, a now-abandoned castle originally built by a rich guy, a lighthouse, and a system of caves only accessible at low tide.
It's really a good thing we know that the Shadow's adventures are true stories transcribed by writer Walter Gibson for publication. Otherwise, we could only assume that Gibson was a wonderful and inventive writer of fiction who creates one of the most perfect settings for a mystery & adventure story ever put down on paper.
Soon, we have a story involves Bron and his ex-smugglers, a gang of presumed German agents, a guy hunting for Blackbeard's buried treasure and two potential damsels-in-distress (a lady who lives in the area and Margo Lane--though both show too much grit to be mere damsels-in-distress). The Shadow and Harry Vincent are also around. There are nighttime ambushes, murder attempts and boat chases coming one after another at a furious pace in a plot that turns out to involve hidden gold buried not by pirates, but by German agents.
The climax involves a sincerely shocking twist involving the supposed motivations of several factions on the island. This all leads to one of the most entertaining action sequences I've ever run across as the Shadow uses the old cannon in the fort to duel with a German U-Boat.
I really love this one. If I were to give you a detailed summary of the plot, I'd give too many spoilers and would also leave the impression that the story is an undisciplined mish-mash of action scenes. But it's not. Taken as a whole, the story has strong internal logic that links all the events together and makes sense out of it all.