Last updated 24 March 2024


Episode Four

Series Episode Number: 321

World Premiere: Sat 29 Apr 1972 - 5:49pm BST [BBC One] (United Kingdom)
First Broadcast: Thu 2 Oct 1975 - 6:30pm CDT [WTTW 11 Chicago]
Running Time: 24 minutes

7.50 Million (UK)


Chart Position: 44 () (UK)

Recorded on Tue 14 Mar 1972 in TC8
Archive State: PAL 2 VT



The Doctor deduces the true meaning of the ancient carvings and must brave the intense radiation of the thaesium caves to retrieve a crystal.


Production Team hide uncredited
WriterBob Baker
WriterDave Martin
DirectorChristopher Barry
ProducerBarry Letts
DesignerJeremy Bear
Script EditorTerrance Dicks
Visual Effects DesignerJohn Horton
Film CameramanFred Hamilton
Film SoundDick Manton
Film EditorDave King
Special SoundBrian Hodgson
Incidental MusicTristram Cary
Title MusicRon Grainer
Title Music BBC Radiophonic Workshop
Fight ArrangerTerry Walsh (uncredited)
Studio LightingFrank Cresswell (uncredited)
Studio SoundTony Millier (uncredited)
CostumesJames Acheson (uncredited)
Make-upJoan Barrett (uncredited)
Production AssistantFiona Cumming (uncredited)
Assistant Floor ManagerSue Hedden (uncredited)
Title Music ArrangerDelia Derbyshire (uncredited)
Title SequenceBernard Lodge (uncredited)
AssistantJoan Elliott (uncredited)
Floor AssistantPhillip Hall (uncredited)
Grams OperatorGordon Phillipson (uncredited)
Vision MixerMichael Turner (uncredited)
Technical Manager(TM2)Clive Leighton (uncredited)