The Fifth Doctor, Tegan and Turlough arrive on Sea Base 4, a nuclear warhead station under the sea that has some very nasty neighbours.
Peter Davison
The Doctor
Janet Fielding
Tegan Jovanka
Mark Strickson
Vislor Turlough
Tom Adams
Vorshak
Ian McCulloch
Nilson
Ingrid Pitt
Solow
Nigel Humphreys
Bulic
Tara Ward
Preston
