Dr. Fu Manchu has been successful in capturing Nyland Smith and Paul Sterling. In his underground laboratories the insidious doctor transforms his prisoners in to members of the Sci-fan by giving them and injection which places them under his will. However Fa Lo Swee renders the injections harmless and while Smith is sent back to the outer world Sterling is assigned to duty inn the botanical research room. here he encounters Dr. Petrie who Smith and Sterling had believed dead but Petrie reveals he had been placed in a state of catalepsy by Fu Manchu. Together they try to escape but are intercepted by Smith who asks them to go back while he surrounds the place with police. Petrie returns to his room and Sterling meets the girl Florette who confesses that she loves him and asks him to escape while there is still time. But suddenly the alarm sounds and in the door appears Dr. Fu Manchu...