The diabolical scheming of the Van Groote Jewelry Company allows them to come into possession of the legendary and cursed Jarvis Devil Diamond. No merchant will go near it, so the diamond brokers plot to have it cut up. To do this, they recruit an experienced diamond cutter, routinely regarded as the greatest gemologist of all time. Having a dubious history, the sage craftsman keeps a low profile by hiding out in San Juan. Innocent dupe Lee (Frankie Darro) is hired by the diamond smugglers to go undercover as a champion boxer. When the gang arrives down south to meet the cutter, a clever undercover insurance adjuster arrives to investigate and the Devil Diamond dealers decide it's every man for himself when violence erupts.