The beheading of international criminal mastermind Dr. Fu Manchu is witnessed in China by his nemesis Nayland Smith. Back in England, however, it is increasingly apparent to Smith that Dr. Fu Manchu is still operating. Despite the skepticism by his close friend Dr. Petrie, Smith is quick to detect that the execution he witnessed was that of a double, an actor hypnotized into taking Dr. Fu Manchu's place. The villain is back in London, and has kidnapped the esteemed Professor Muller, whose research holds the key to a potentially deadly solution from the seeds of a rare Tibetan flower: the Blackhill poppy. The seed of this poppy is sometimes referred to as "The Seed of Life", and Tibetans spoke legends of it being the secret to eternal life. Although the poppy seed's poison loses its toxicity when exposed to heat, Fu Manchu has heard Tibetan legends that the poison was once weaponized. A pint of this poison is powerful enough to kill every person and animal in London.