Prior to the beginning of World War II, the Nazis, at the request of Japan's Black Dragon Society, sends Doctor Melcher (Bela Lugosi) to Japan to transform six Japanese into identical likenesses of six prominent Americans. The Americans are done away with and Melcher, on the orders of High Dragon Yakhamea (I. Stanford Jolley), is imprisoned so his secret will die with him. In his cell, Melcher switches places with the soon-to-be-released Colomb and, when he is freed, follows the six Japanese to America, where they have assumed the positions of the industrialists and are causing sabotage in the Monogram defense plants that didn't exist yet as the war hadn't started. One by one Melcher kills the imposters, despite the fact they are performing for-free work for his employer Adolph, and dumps their bodies on the steps of the Japanese Embassy, which still existed as the war hadn't started. FBI Chief Colton (Kenneth Harlan) and agent Dick Martin (Clayton Moore) finally piece together what the five murdered men had in common---aha, a visit to Japan---and stake out the sixth man as bait for Melcher.