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Peter Davison
The Doctor

Sarah Sutton
Nyssa

Janet Fielding
Tegan Jovanka

Mark Strickson
Vislor Turlough

Nicholas Courtney
Brigadier Alistair Gordon Lethbridge-Stewart

Valentine Dyall
The Black Guardian

David Collings
Mawdryn

Angus MacKay
Headmaster

Stephen Garlick
Ibbotson

Roger Hammond
Dr. Runciman

Sheila Gill
Matron

Peter Walmsley
Mutant

Brian Darnley
Mutant

William Hartnell
The Doctor (1) (archive footage)

Patrick Troughton
The Doctor (2) (archive footage)

Jon Pertwee
The Doctor (3) (archive footage)