Gentleman crook Boston Blackie answers a want ad for an expert safe cracker placed by Doris Macon, who claims a moral right to the safe's contents. She hires Blackie, and they break into the house where the safe is kept. Blackie blows up the safe just as owner Captain von Hoffmeier returns home. Doris disappears with papers from inside the safe, while Blackie takes phonograph records, which, when played with a special needle, reveal secrets that implicate von Hoffmeier as a German political spy. Doris is actually the girl friend of a secret service man who has followed them to the house. Blackie's talents are praised, and he goes to work for the government.—AFI