Last updated 24 March 2024


Part One

Series Episode Number: 603

World Premiere: Thu 5 Jan 1984 - 6:41pm GMT [BBC One] (United Kingdom)
First Broadcast: Fri 7 Dec 1984 - 11:00pm CST [WTTW 11 Chicago]
Running Time: 24 minutes 48 seconds

7.60 Million (UK)

Appreciation Index: 65 (UK)

Chart Position: 51 () (UK)




Seabase 4 is on alert as a strange craft approaches. But the crew has been infiltrated by the enemy, so Commander Vorshak's solutions are scuppered at every turn.


Characters hide uncredited
The DoctorPeter Davison
TeganJanet Fielding
TurloughMark Strickson
VorshakTom Adams
SolowIngrid Pitt
NilsonIan McCulloch
MaddoxMartin Neil
PrestonTara Ward
IctharNorman Comer
KarinaNitza Saul
ScibusStuart Blake
TarpokVincent Brimble
SauvixChristopher Farries
ParoliJames Coombes
Stunt Double for The DoctorGareth Milne (uncredited)
Marine/GuardJulian Hudson (uncredited)
Marine/GuardBarney Lawrence (uncredited)
Marine/GuardPeter Caton (uncredited)
Marine/GuardDana Miche (uncredited)
Marine/GuardJulian Larousse (uncredited)
Marine/GuardRose Pridmore (uncredited)
Marine/GuardDorothy Ottey (uncredited)
Marine/GuardRidgewell Hawkes (uncredited)
Marine/GuardTrevor Steedman (uncredited)
Sea Base PersonnelJoanna Garcia (uncredited)
Sea Base PersonnelLing Tai (uncredited)
Sea Base PersonnelJoycea Goborn (uncredited)
Sea Base PersonnelArnold Lee (uncredited)
Sea Base PersonnelRussell Brook (uncredited)
Sea DevilSteve Kelly (uncredited)
Sea DevilChris Wolff (uncredited)
Sea DevilJules Walters (uncredited)
Sea DevilMike Brayburn (uncredited)
Sea DevilDave Ould (uncredited)
Production Team include uncredited
WriterJohnny Byrne
DirectorPennant Roberts
ProducerJohn Nathan-Turner
DesignerTony Burrough
Script EditorEric Saward
Title SequenceSid Sutton
Costume DesignerJudy Pepperdine
Make-up ArtistJennifer Hughes
LightingPeter Smee
SoundMartin Ridout
Technical ManagerAlan Arbuthnott
Camera SupervisorBob Baxter
Camera SupervisorAlec Wheal
Videotape EditorHugh Parson
Visual Effects DesignerMat Irvine
Video EffectsDave Chapman
Vision MixerNigel Finnis
Technical Manager(TM2)Alan Woolford
OB Camera SupervisorAlastair Mitchell
OB SoundChris Holcombe
Production ManagerMichael Darbon
Production AssociateJune Collins
Production AssistantNorma Flint
Assistant Floor ManagerAdrian Hayward
Incidental MusicJonathan Gibbs
Special SoundDick Mills
Title Music BBC Radiophonic Workshop
Special Sound BBC Radiophonic Workshop