Most of the people of Llanfairfach, Wales, welome Global Chemical's new refinery, but some people are not so happy, and a group of ecologists, lead by Professor Clifford Jones, oppose the plant. When a miner in a Welsh village is found dead, his skin glowing green, U.N.I.T. are called in to investigate.
The Doctor investigates the mines, and finds a group of giant green maggots, and green slime pumped into the mine from the refinery. Meanwhile Jo has fallen in with the ecologists, and looks at some of their work, which includes a form of fungus that can be used to make a variety of different foods.
When the refinery director, Stevens, is confronted by the Doctor and U.N.I.T. he refuses to comment. The Doctor later uses a disguise to enter the factory and find out what is on the top floor. There he finds the real controller of the refinery - BOSS - a giant computer who has taken over the mind of Stevens.
BOSS plans to take over the world by linking itself to every other computer in the world. Using a crystal which he got from Metebelis 3 the Doctor manages to break the computer's hold over Stevens, who reprograms it to self-destruct. They find out by accident that the giant maggots can be killed using Professor Jones's fungus, and eventually they are all destroyed.
Professor Jones tells of an expedition he is planning down the Amazon, and asks Jo to go with him. Jo accepts, and parts company with the Doctor and U.N.I.T.
Regular castBrigadier Lethbridge-Stewart: Nicholas Courtney; Sergeant Benton: John Levene; Jo Grant: Katy Manning; Captain Yates: Richard Franklin;
Guest castStevens: Jerome Willis; Professor Clifford Jones: Stewart Bevan; Elgin: Tony Adams (1-4); Hinks: Ben Howard (1-4); Nancy: Mitzi McKenzie (1,3-6); Milkman (Jones the Milk): Ray Handy (1,4); Dai Evans: Mostyn Evans (1-2); Dave Davies: Talfryn Thomas (1-3); Bert Pritchard: Roy Evans (1-2); Ted Hughes: John Scott Martin (1); BOSS's Voice: John Dearth (2-6); Ralph Fell: John Rolfe (2-3); Guard of Main Gate: Terry Walsh (2,4,6 - uncredited 6); Security Guards: Billy Horrigan (2), Alan Chuntz (2); Minister of Ecology: Richard Beale (3); Cleaner (Doris Griffiths): Jean Burgess (4); Yates's Guard: Brian Justice (4); James: Roy Skelton (5 + reprise 6);
Uncredited cast: Miners: Frank Seton (1-3), David Waterman (1-3); Villagers: Reg Cranfield (1), Sonny Willis (1); Global Chemical's Tannoy Voice: John Dearth (2-5); UNIT Radio Voices: John Dearth (2,5,6); Cabinet Minister: Evan Ross (3); Prime Minister (Sir Jeffrey): Brychan Powell (3); Hippy Boy: Robert Birmingham (3); Lotus Position Girl (Elda): Jean Channon (3); Hippy Girl: Alison Daumler (3); Sculptor: Ken Hanniwell (3); Long-haired Boy: Keith Norrish (3); Girl: Lyn Melly (3); Flautist (Jessie): Stanley Clarke (3); UNIT Men: Leslie Bates, David Billa; Security Guards: Leslie Bates, Alan Chuntz, Pat Gorman, Billy Horrigan, Steve Ismay, Dennis Plenty, Terry Walsh; Extras: Jill Alexandra, Laurie Boyton, David Braddick, Gordon Cecil, Michael Cunningham, Frank Darroch, Vincent Gardener, John Jeffries, Geoffrey Morgan, Rendle Morris, Roger Mundy, Tricia Selby, Wayne Warlow, Mansel Wilks;
|BBC 1||350||Episode One||Sat 19 May 1973||5:50 pm - 6:15 pm||9.2M||18th|
|BBC 1||351||Episode Two||Sat 26 May 1973||5:50 pm - 6:15 pm||7.2M||38th|
|BBC 1||352||Episode Three||Sat 2 June 1973||5:50 pm - 6:15 pm||7.8M||29th|
|BBC 1||353||Episode Four||Sat 9 June 1973||5:50 pm - 6:15 pm||6.8M||32nd|
|BBC 1||354||Episode Five||Sat 16 June 1973||5:50 pm - 6:15 pm||8.3M||15th|
|BBC 1||355||Episode Six||Sat 23 June 1973||5:50 pm - 6:15 pm||7.0M||30th|
Repeats (on the BBC)
'Scotch' factory, Merthyr Tydfill, Mid Glamorgan; Deri, Mid Glamorgan;
Television Centre Studio 3;
Bloopers and mistakes
Episode 2: After the lift brake fails at the start of the episode, a close-up shot of Katy Manning shows her miner's helmet lacking a lamp. But in the next shot, the lamp magically returns.
Episode 2: In the fight scene with the security guards, Pertwee's double is wearing the wrong colour wig.
Episode 2: When the Brigadier phones Professor Jones looking for cutting equipment to rescue Jo and Bert from the mine, Jones suggests asking Global Chemicals instead, since he tried to borrow some from them several weeks ago. But when the Brigadier is talking to Stevens at Global Chemicals and mentions the Professor, Stevens says something like: "Ah yes, he came looking for our cutting equipment yesterday."
Notes and trivia
Katy Manning leaves at the end of the story.
The end title pattern is upside-down for Episodes Two, Five and Six. The end of Episode Six fades slowly into the end credits.
This programme has no other working titles, or they have not been yet been entered.