Cajun box man known as Duval blows a safe in San Francisco and makes off with sixty thousand dollars in diamonds and precious stones. Insurance Company of North America engages Colonel David Crook's Great Western Detective League. Veteran investigators Beau Longstreet and Briscoe Cane take the case. The Jeweler's Protective Association turns to the Pinkerton Agency. Partnered with the ultra-secret criminal syndicate El Anillo, the real money from the heist is made selling unsuspecting investors shares in the mine from which the jewels were taken. The investigation crosses and double-crosses from bribery to jailbreak to murder and abduction before the pursuit twists and turns to an explosive climax in the syndicate's lair.