In the distant future, the Doctor, Sarah and Harry find a space station preserving the future of mankind. But the insect Wirrn have got there first...
Tom Baker
as The Doctor
Elisabeth Sladen
as Sarah Jane Smith
Ian Marter
as Harry Sullivan
Wendy Williams
as Vira
Kenton Moore
as Noah
Richardson Morgan
as Rogin
John Gregg
as Lycett
Christopher Masters
as Libri
Stuart Fell
as The Wirrn
Nick Hobbs
as The Wirrn
Gladys Spencer
as High Minister (voice)
Peter Tuddenham
as Voices on Nerva (voice)
