22 March 1982
Richard Easton (Captain Stapley), Keith Drinkel (Flight Engineer Scobie), Michael Cashman (First officer Bilton), Peter Dahlsen (Horton) [1, 4], Brian McDermott (Sheard) [1, 4], John Flint (Captain Urquhart) , Peter Cellier (Andrews) , Judith Byfield (Angela Clifford), Leon Ny Taiy (Kalid) *, Nigel Stock (Professor Hayter) [2-4], Anthony Ainley (The Master) [2-4], Hugh Hayes (Anithon)  André Winterton (Zarak) [3-4], Matthew Waterhouse (Adric)
|Written by||Peter Grimwade|
|Directed by||Ron Jones|
|Produced by||John Nathan Turner|
When a Concorde disappears, The Doctor discovers that it has been hijacked back through time to the Pleistocene Era. Arriving there, he, Nyssa and Tegan find that Concorde’s crew and passengers have been enslaved by the sinister Kalid, who is forcing them to excavate a sanctum within a mysterious citadel.
Entombed within is the consciousness of a gestalt race called the Xeraphin, who possess devastating mental powers. The Doctor learns that Kalid is really The Master, who plans to harness the evil side of the Xeraphin in order to wreak havoc throughout the cosmos.
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