- Edward Petherbridge - Mullins
- Joyce Carey - Lady with Dog
- Robert Gillespie - Frank Goff
- Derek Waring - George Harmer
- Peter Copley - Prof. Waterlow
- Bruce Purchase - Prof. Lopez
- Robert Flemyng - Minister Quaintance
- Bruce Bould - Froggart
- Vladek Sheybal - Zarcardi
- Anna Palk - Suzy
- Lyndon Brook - Cartney
- Pik-Sen Lim - Sing
- Ian Hendry - Irwin Gunner
- Robert Beatty - Col. Ilenko
- Sammie Winmill - Molly (uncredited)
- Davina Taylor - Tricia
- Jenny Runacre - Irene Brandon
- J.G. Devlin - Tramp
- Gary Waldhorn - Roach
- Frank Thornton - Roland
- Roy Boyd - Fred Bradshaw
- Jo Kendall - Nurse
- Sydney Bromley - Hara
- Donald Hewlett - Torrance
- Ed Devereaux - Vann
- David Horovitch - Tom Fitzroy
- Gordon Rollings - Bridlington
- John Paul - Dr. Kendrick
- Robert Lang - Felix Kane
- Hugh Walters - Lewington
- Geoffrey Toone - Minister
- Jerold Wells - Barker
- Edward Judd - Cromwell
- Jeremy Child - Lieutenant
- Richard Leech - Craig Terrison
- Annette Andre - Suzy Miller
- John Carson - Freddy
- Basil Dignam - Hugh Rydercroft
- Malcolm Stoddard - George Myers
- Michael Sheard - Peters
- Roy Marsden - Frank Turner
- Derek Farr - Father Trasker
- Gwen Taylor - Doctor Marlow
- Mark Burns - Spence
- Anthony Sharp - Grant
- Sally-Jane Spencer - Mother
- George A. Cooper - Burt Brandon
- Peter Cushing - Von Claus
- Ronald Lacey - Hong Kong Harry
- Pearl Hackney - Mrs. Weir
- Kevin Stoney - Tomkins
- Keith Barron - Draker
- Derek Francis - The Bishop
- Trevor Baxter - Brown-Fitch
- Oscar Quitak - Malov
- Bernice Stegers - Operator
- Peter Jeffrey - Ivan Perov
- Frederick Jaeger - Jones
- Jeremy Wilkin - Dr. Tulliver
- Basil Hoskins - Professor Mason
- Sally Bazely - Laura
- Anthony Bailey - Frederick
- Sidney Hayers
- Desmond Davis
- John Hough
- Graeme Clifford
- Claude Fournier
- Ray Austin
- Brian Clemens
- Dennis Spooner
- John Goldsmith
- Terence Feely
Peter Cushing interpreta a Von Claus en la serie.
Ronald Lacey interpreta a Hong Kong Harry en la serie.
Robert Beatty interpreta a Col. Ilenko en la serie.
Patrick Macnee interpreta a John Steed en la serie.
Gareth Hunt hace el papel de Mike Gambit.
Joanna Lumley interpreta a Purdey en la serie.
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