A Scotland Yard investigator assists a determined associate in decoding a doggerel cryptogram that conceals the combination to a massive safe containing a deceased man’s fortune. When the will names four possible beneficiaries, two violent members of a notorious gang try to seize the prize, sparking a race of detection, break-ins, and counterplots. The narrative follows efforts to secure and open the fortified deposit, inquiries into its construction and the cryptogram, and escalating clashes between investigative craft and criminal aggression, culminating in the revelation of the safe’s secret and the settlement of competing claims.