In an effort to trap Fu Manchu Nyland Smith has transferred Florette and Sterling who are still under the influence of an unknown drug to a room in the Hospital du Jardin. Convinced that the insidious doctor is going to make every effort to capture Florette Smith conceals himself in the room and awaits developments. While Petrie and Karamay are watching over the patients Dr. FU Manchu enters and forces Petrie to administer an injection which he claims will release them from the paralyzing drug. When Smith confronts his enemy the oriental escapes through an ingeniously hidden trap door and Smith realizing that the only avenue of escape left is the submarine, once again boards the destroyer. He detects the undersea craft and by means of death bombs forces his adversary to the surface. Upon boarding the craft he finds dr. FU in command and submitting to arrest the insidious doctor is taken to French prison. Leaving Weymouth in charge at the prison Smith returns to the hospital and...