On a rainy evening, Bulldog Drummond finds himself in the arms of a dame as they stay dry in a book store. The gun in her hand is enough to convince him to do as she says in finding a book that holds a secret message. Who was the stranger who was following her? Is the book store owner involved somehow? After being roughed up, and the recipient of a thump on the head, Drummond finds himself in a cab with a body.
The corpse is taken home with Drummond to be handed over to the police. The mysterious blonde dame is back, but will she know anything about the dead man? Instead, she tells about a jealous husband, and a plan for blackmail against her.
Wilson claims to be from the Treasury Department, and is on the trail of Mrs Oltman. The dame makes a get away, taking the book that Drummond was forced to pick up for her… or did she get it? Drummond pursues the importance of the book, but a killer seems to be a step ahead of him. A photography dark room set up leads Drummond to find the secret of the book. But wait, there’s more secrets to be exposed as secret codes are cracked. Counterfeit bills, T-men, spies, nobody is as they seem. Thanks to fingerprint clues, Drummond is able to save the day.