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.
| Actor | Role |
|---|---|
 Peter SellersFu Manchu / Nayland Smith | Fu Manchu / Nayland Smith |
 Helen MirrenAlice Rage | Alice Rage |
 David TomlinsonSir Roger Avery | Sir Roger Avery |
 Sid CaesarJoe Capone | Joe Capone |
 Simon WilliamsRobert Townsend | Robert Townsend |
 Steve FrankenPeter Williams | Peter Williams |
 Stratford JohnsIsmail | Ismail |
 John Le MesurierPerkins | Perkins |
| JJohn SharpSir Thuud | Sir Thuud |
 Clément HarariDr. Wretch | Dr. Wretch |
 Kwan-Young LeeTang | Tang |
 Burt KwoukFu Manchu's Servant | Fu Manchu's Servant |
 Derek MartinMuseum Guard | Museum Guard |
 Philip TanDacoit | Dacoit |
 Clive DunnKeeper of the Keys - London Tower | Keeper of the Keys - London Tower |