Fu Manchu's 168th birthday celebration is dampened when a hapless flunky spills Fu's age-regressing elixir vitae. Fu sends his lackeys to round up ingredients for a new batch of elixir, starting with the Star of Leningrad diamond, nabbed from a Soviet exhibition in Washington. The FBI sends agents Capone and Williams to England to confer with Nayland Smith, an expert on Fu. Nayland suspects Fu will kidnap the king and queen and demand the George V diamond as ransom. Scotland Yard recruits Alice Rage to stand-in for the queen. Fu nabs the "fake" queen; Rage becomes enamored of Fu and aids him in his quest for the George V diamond.