Last updated 09 January 2020


Part Four

Series Episode Number: 443

World Premiere: Sat 22 Jan 1977 - 6:26pm GMT [BBC One] (United Kingdom)
First Broadcast: Mon 26 May 1980 - 5:30pm CDT [WTTW 11 Chicago]
Running Time: 24 minutes 46 seconds

11.70 Million (UK)

Appreciation Index: 60 (UK)

Chart Position: 19 () (UK)

Recorded on Tue 26 Oct 1976 in TC3
BBC Genome Project: see entry



Determined to rectify his earlier mistake, the Doctor tries to repair Xoanon. But the insane computer refuses to accept his help and prepares to destroy the entire planet.


Production Team hide uncredited
WriterChris Boucher
DirectorPennant Roberts
ProducerPhilip Hinchcliffe
DesignerAustin Ruddy
Script EditorRobert Holmes
Costume DesignerJohn Bloomfield
Make-up ArtistAnn Ailes
Visual Effects DesignerMat Irvine
Special SoundDick Mills
LightingDerek Slee
SoundColin Dixon
Title SequenceBernard Lodge
Production AssistantMarion McDougall
Production Unit ManagerChris D'Oyly-John
Incidental MusicDudley Simpson
Title MusicRon Grainer
and the BBC Radiophonic Workshop
Fight ArrangerTerry Walsh
Assistant Floor ManagerRichard Leyland (uncredited)
Vision MixerJames Gould (uncredited)Info
Grams OperatorGordon Phillipson (uncredited)
TM2Ron Bristow (uncredited)
Floor AssistantPhilip Livingstone (uncredited)Info
Inlay OperatorDave Chapman (uncredited)
Senior CameramanColin Reed (uncredited)
Director's AssistantSue Ward (uncredited)
Props BuyerBrenda Barker (uncredited)
Props BuyerVal Woodford (uncredited)
Post-Production GramsMike Felton (uncredited)
Post-Production GramsR. Williams (uncredited)
Post Production SoundDerek Miller-Timmins (uncredited)
Make-Up AssistantJennifer Hughes (uncredited)
Make-Up AssistantSue Frear (uncredited)
Make-Up AssistantKaren Bryan (uncredited)
Make-Up AssistantCarol Wilson (uncredited)
Production SecretaryAnn Rickard (uncredited)
Artist BookingNansi Davies (uncredited)
Title Music ArrangerDelia Derbyshire (uncredited)