Through the quick actions of Nayland Smith, Sean Grebble and Superintendent Weymouth and a cordon of police escaped disaster when a powder keg concealed by a gypsy camp wagon exploded. Later back in London Grebble meets the mysterious Dr Amber who proves to be Lee Kin Su, Chief assistant to Dr Fu Manchu. Lee warns Grebble of grave danger to Smith at the hands of Fu Manchu's daughter and Grebble hurrying back to his hotel is kidnapped...