31 January 1976
Tony Beckley (Harrison Chase) John Challis (Scorby) Mark Jones (Arnold Keeler) [1-4], Hubert Rees (John Stevenson) [1-2], John Gleeson (Charles Winlett) [1-2], Michael McStay (Derek Moberley) [1-2], Kenneth Gilbert (Richard Dunbar) [1-4], Michael Barrington (Sir Colin Thackeray) [1,3-6], Seymour Green (Hargreaves) [1,3-5], Sylvia Coleridge (Amelia Ducat) [3-5], David Masterman (Guard Leader) [3-4], Ian Fairbairn (Doctor Chester) , Alan Chuntz (Chauffeur) , Harry Fielder (Guard) *, John Acheson (Major Beresford) [5-6], Ray Barron (Sergeant Henderson) [5-6], Mark Jones (The Krynoid’s Voice) 
|Written by||Robert Banks Stewart|
|Directed by||Douglas Camfield|
|Produced by||Philip Hinchcliffe|
An Antarctic expedition unearths two pods which the Doctor recognises as Krynoids. Once germinated, the pods will infect humans, turning them into giant carnivorous plants which will quickly overrun the world. The Doctor and Sarah Jane manage to destroy one Krynoid, but the other is stolen by an insane botanist named Harrison Chase, who intends to use the alien entity to help plants take over the world.
- Episodes 1 and 2 are heavily influenced by Howard Hawks’ 1951 film
- The Thing From Another World: An artifact found frozen in the Antarctic ice is revealed to be a deadly plant-like alien.
- The film was itself based on the short story, “Who Goes There?,” written by John W. Campbell, Jr. Others have noticed a strong similarity between this story and “Man-Eater of Surrey Green,” an installment of The Avengers television series of the 1960s, and also the 1953 BBC production The Quatermass Experiment.
- The serial also marked the final major appearance of UNIT in the series until 1989’s Battlefield (although it would be referenced in the Fifth Doctor story Time-Flight,Brigadier Alistair Gordon Lethbridge-Stewart appeared in the 1983 story Mawdryn Undead as a retired civilian, and there is a sequence set at UNIT HQ in The Five Doctors).
- None of the established UNIT characters are seen in UNIT‘s brief appearance in this story, as it was felt that there was too little material to warrant bringing back the Brigadier and Sergeant John Benton. Although the Doctor worked with UNIT in later stories (continuing into the mid-2000s revival), this is the last story to date in which the Doctor is explicitly shown to be working for UNIT.
- The story was director Douglas Camfield’s last involvement with Doctor Who. Camfield went on to direct other television programs and died in his sleep in 1984.
- A few weeks before the serial was due to begin its original transmission, the master tape for the first episode was found to be missing.
- A brief panic ensued and producer Philip Hinchcliffe began planning a re-edit of the second episode allowing the story to begin at this point, but fortunately the tape of the opening episode was eventually located, having been misplaced in the tape storage system (apparently due to having been wrongly numbered).
- The costume for the humanoid stage of the Krynoid was created by taking one of the surviving Axon costumes from The Claws of Axos and spraying it green.
- The name ‘Krynoid’ would appear to be adapted from ‘crinoid’, a small flower-like creature, related to star fish and sea urchins, that live in shallow and deep oceans worldwide.
- This serial was the last serial to use the Brachacki police box prop, as it finally wore out and collapsed — reportedly while Tom Baker and Elisabeth Sladen were inside.
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