The Doctor and Jo attend a demonstration of the Keller Machine at Stangmoor Prison; it is claimed that the machine can extract negative emotions. The Doctor is sceptical, and this seems justified when a prisoner collapses during treatment.
The Brigadier has problems of his own: U.N.I.T. are providing security for the World Peace Conference when documents go missing, and the Chinese delegate is found dead. At the same time Captain Yates is in charge of taking a Thunderbolt missile to be destroyed.
The Doctor and Jo join the Brigadier, and manage to stop the Chinese delegate's aide, Captain Chin Lee, from killing the American delegate. Lee is actually under the control of the Master, who is assuming the guise of Emil Keller.
The Master is using the stored negative emotions from the Keller Machine to cause unrest at the prison, and then uses the convicts to sieze the missile with the aim of destroying the peace conference. The Doctor manages to activate the missile's auto-destruct. The emotions container and machine are presumed destroyed, but the Master escapes ...
Regular castBrigadier Lethbridge-Stewart: Nicholas Courtney; Sergeant Benton: John Levene; Jo Grant: Katy Manning; Captain Yates: Richard Franklin;
Guest castGeorge Barnham: Neil McCarthy (1-3,5-6); Corporal Bell: Fernanda Marlowe (1-4); Doctor Roland Summers: Michael Sheard (1-4); Prison Governor (Major Victor Camford): Raymond Westall (1-3); Captain Chin-Lee: Pik-Sen Lim (1-3); Chief Prison Officer Powers: Roy Purcell (1-3); Senior Prison Officer Green: Eric Mason (1-3); Professor Charles Kettering: Simon Lack (1); Arthur Linwood: Clive Scott (1); The Master: Roger Delgado (2-6); Harry Mailer: William Marlowe (2,5 - reprise 6); Lennie Vosper: Haydn Jones (2-4); Fu Peng: Kristopher Kum (2-3); Senator Alcott: Tommy Duggan (2); Prison Officers: Dave Carter, Martin Gordon, Bill Matthews, Barry Wade; Charlie: David Calerisi (4);; Major Cosworth: Patrick Godfrey (5-6); Fuller: Johnny Barrs (5); Main Gate Prisoner: Matthew Waltes (5);
Uncredited cast: Police Superintendent: Paul Blomley (1); Photographers: Stuart Fell (1), Charles Marriott (1); General Cheng Teik: Francis Batsoni (1); African Delegate/The Master's Chauffeur: Francis Williams; American Aide: Nick Hobbs (2); UNIT Corporal: Billy Horrigan (2); Voices on Telephone (UNIT Transport Division): Laurence Harrington (2); Chinese Aide: Paul Tann (2); Passerby: Jim Delaney (2); Female Student: Maureen Race (2); Police Inspector: Richard Atherton (4); Prison Officers: Richard Atherton, Les Clark, Les Conrad, Tony Jenkins, Gordon Stoppard, Leslie Weeks; Prisoners/Audience: Richard Atherton, Denis Balcombe, George Ballentine, Francis Batsoni, Paul Blomley, Marc Boyle, Michael Carter, Alan Chuntz, Les Clark, Les Conrad, Billy Horrigan, Nad Hood, Leonard Kingston, Roger Marsden, Alistair McFarlane, Valentino Musetti, Mike Stevens, Cy Town, Wolfgang Van Jergen, Desmond Verlini, Matthew Walters, Phillip Webb; Medical Officers: Charles Finch, Charles Pickess, Cy Town; UNIT Soldiers and Staff: Denis Balcombe, Stuart Fell, Nick Hobbs, Charles Marriott, Roger Marsden; Extras: Laurie Ayres, Denis Balcombe, Robert Bald, Bob Blaine, Frank Bennett, Michael Carter, Derek Chafer, Johnny Clump, Timothy Combe, Max Diamond, Pat Donohue, Ian Elliott, Gary Gregory, PG Heath, Tony Jenkins, Ricky Lancing, Derek Martin, Roy Scammell, Mike Stevens, Terry Walsh and Lance Bombadier R Berkley, Gunner K Davenport, Bombadier A Graham, Bombadier Barry Hall, Sergeant Herridge, Bombadier J Lamb, Sergeant D Talbot, Bombadier R. Thompson;
|BBC 1||283||Episode One||Sat 30 January 1971||5:15 pm - 5:40 pm||9.2M||61st|
|BBC 1||284||Episode Two||Sat 6 February 1971||5:15 pm - 5:40 pm||8.8M||54th|
|BBC 1||285||Episode Three||Sat 13 February 1971||5:15 pm - 5:40 pm||7.5M||70th|
|BBC 1||286||Episode Four||Sat 20 February 1971||5:15 pm - 5:40 pm||7.4M||63rd|
|BBC 1||287||Episode Five||Sat 27 February 1971||5:15 pm - 5:40 pm||7.6M||58th|
|BBC 1||288||Episode Six||Fri 5 March 1971||5:15 pm - 5:40 pm||7.3M||65th|
Dover Castle, Kent; Kensington, London;
Television Centre Studio 3;
Bloopers and mistakes
Episode 3: After the Master has the Doctor brought to the prison office, he informs him that he intends to steal a nuclear weapon from U.N.I.T. to blow up the World Peace Conference. As has already been firmly established in the previous two episodes, it is a nerve gas missile; the Master himself even heard this information from having tapped the phones at HQ.
Episode 3: As the Doctor and the Master have a fist-fight in the prison governor's office they knock over a water carafe, and slip and slide all over the ensuing puddle. This wasn't meant to happen, but they kept it in the finished episode, just because it looked great.
Notes and trivia
This is the only colour story where all of the episodes are only held by the BBC in black and white.
Pandora's Box; The Pandora Machine;