A skilled safecracker emerges from a long prison term and is immediately enveloped in a web of theft, coded secrets, and police scrutiny. The plot follows his uneasy freedom as Scotland Yard detectives track a string of bold robberies tied to an enigmatic cipher, interweaving clandestine meetings, betrayals within criminal ranks, and methodical investigative work. The narrative builds to a revealing solution that uncovers how the cipher operated and who profited from the conspiracies.