When scientists in the Antarctic uncover a mysterious seed pod, the Doctor is called in to investigate. He soon realises it is extraterrestrial and extremely dangerous. At the same time, however, ruthless millionaire plant-lover Harrison Chase has learned of the find and decides he must have the pod for his collection of rare and beautiful flora. Meanwhile the pod itself harbours intelligent life with sinister plans of its own...
Tom Baker
as The Doctor
Elisabeth Sladen
as Sarah Jane Smith
Tony Beckley
as Harrison Chase
Kenneth Gilbert
as Richard Dunbar
Michael Barrington
as Sir Colin Thackeray
Sylvia Coleridge
as Amelia Ducat
John Challis
as Scorby
Mark Jones
as Arnold Keeler / Krynoid (voice)
Seymour Green
as Hargreaves
Michael McStay
as Derek Moberley
Hubert Rees
as John Stevensen
John Gleeson
as Charles Winlett
