Shang-Chi finds an ally in Fu Manchu's old enemy Sir Denis Nayland Smith and learns that Fu Manchu is smuggling a secret cargo into Florida. The cargo consists of gasoline laced with mimosa, a sedative intended to pacify the population and facilitate Fu Manchu's take-over of the United States. Shang-Chi is captured and foced to fight the doped-up dacoit Satma, but in the end he is able to escape and destroy the gasoline shipment.