Fu Manchu’s (Peter Sellers’) 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, D.C. The F.B.I. sends Agents Joe Capone (Sid Caesar) and Pete Williams (Steve Franken) to England to confer with Sir Dennis Nayland Smith (Peter Sellers), an expert on Fu. Nayland suspects Fu will kidnap King George V (Rene Aranda) and Queen Mary (Grace Coyle) and demand the George V diamond as ransom. Scotland Yard recruits Alice Rage (Dame Helen Mirren) 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.