 In Tibet, following the First World War, American Lamont Cranston, succumbing to his dark instincts, sets himself up as a warlord and opium kingpin under the alias of "Yin-Ko" (said to mean "Dark Eagle" in a Mandarin Chinese dialect).He is abducted by servants of the Tulku, a holy man who exhibits otherworldly powers and knows Cranston's identity.He offers Cranston a chance to redeem himself and become a force for good.