The Doctor and Sarah respond to a distress signal emanating from the planet Zeta Minor, at the very edge of the universe. There they discover that a research team has been systematically hunted down by an invisible anti-matter monster. The only survivor is Professor Sorenson, who has discovered a mineral which could serve as an almost limitless power source. When a rescue mission led by Salamar also arrives on Zeta Minor, the time travellers find themselves accused of murdering the scientific expedition. The Doctor must find a way to convince Salamar of the truth before Sorenson, corrupted by the anti-matter, dooms them all.

When they began planning for Doctor Who's thirteenth season, producer Philip Hinchcliffe and script editor Robert Holmes agreed that the programme had spent too much time on Earth in recent years. To this end, they engaged designer Roger Murray-Leach in preliminary discussions about creating a truly alien environment within the confines of the BBC Television Film Studios at Ealing, London. Murray-Leach had designed three serials for Season Twelve -- most notably The Ark In Space -- and both men had been impressed with his work.

For the story which would make use of the proposed sets, Hinchcliffe suggested taking inspiration from the 1956 science-fiction classic Forbidden Planet, which he had enjoyed in his youth. Whereas the film had seen a monster revealed to be the embodiment of the dark side of a scientist's mind, Hinchcliffe suggested the notion of a monster which represented the malign aspects of a planet. Holmes, for his part, was interested in an adventure which drew upon Robert Louis Stevenson's seminal 1886 novel Strange Case Of Dr Jekyll And Mr Hyde, in which an experiment caused a good-natured scientist to transform into a violent, debased alter ego.

The scripts' jungle environment would provide Roger Murray-Leach with considerable freedom in his design work

To write such a serial, Holmes approached Louis Marks, with whom he had previously worked on several occasions. Marks had twice contributed to Doctor Who in the past, most recently scripting Day Of The Daleks in 1971. It was decided that Marks' scripts would be set in a jungle environment; this would contrast with the barren world of Forbidden Planet, and provide Murray-Leach with considerable creative freedom in his design work. Marks, who was under contract to the BBC as a script editor, received staff clearance for his Doctor Who work on May 19th, 1975; in reality, he had begun writing them much earlier in the year.

Marks' adventure came to be called Planet Of Evil, although “The Planet Of Evil” was also employed on occasion. While scheduled for production after Pyramids Of Mars, it would be transmitted first in order to give Season Thirteen a better balance between stories set on Earth and in space, and between those recorded on location and in studio. Shortly before production began, Hinchcliffe requested an amendment to the closing moments of Planet Of Evil. In Marks' original version, Sorenson did not reappear after plunging into the black pool. Hinchcliffe felt that this was not a suitable fate for a well-intentioned character, and so Holmes rewrote the ending to have Sorenson survive.

Assigned to direct Planet Of Evil was David Maloney, who had recently completed work on the previous season's Genesis Of The Daleks. As hoped, Murray-Leach was brought aboard as the serial's designer. With no location filming allocated to the production, Murray-Leach was given the freedom to design a fabulously detailed, exotic and alien jungle set at Ealing to represent the surface of Zeta Minor, for filming on June 11th and 12th. This set proved so successful that it was extensively photographed by the BBC Educational Service, which would use it as an example of design excellence for years afterwards. Nonetheless, some problems did result: in particular, it was virtually impossible to appropriately position sound booms, which meant that much of the dialogue had to be redubbed. Work at Ealing continued on June 13th, when scenes in the void were filmed. Model shots were also completed there on the 17th.

As usual, studio recording for Planet Of Evil took place in fortnightly blocks on Mondays and Tuesdays. The first of these, at BBC Television Centre Studio 6 in White City, London, encompassed June 30th (for most of Episode One) and July 1st (for Episode Two). The second session occurred on July 14th and 15th, this time in TC3. The Monday dealt with Episode Three, plus the TARDIS sequences for Episode One. The Tuesday was entirely devoted to the serial's concluding installment.

The first three episodes of Planet Of Evil were preceded by Walt Disney's The Mouse Factory and a news update, and followed by the new season of Bruce Forsyth And The Generation Game. On October 11th, the entire evening schedule -- including Planet Of Evil Episode Three -- was delayed by twenty minutes to accommodate an extra-length edition of Grandstand, which was marking its one-thousandth broadcast. The following week, Doctor Who obtained a new lead-in as The Basil Brush Show replaced the Disney programme. This version of the BBC Saturday schedule would later be fondly remembered as a television classic.

• Doctor Who Magazine #183, 19th February 1992, “Archive: Planet Of Evil” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #8, 1st September 2004, “Bohemian Rhapsody” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #24, 2016, “Story 81: Planet Of Evil”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Fourth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.
• In·Vision #8, September 1988, “Production” edited by Justin Richards and Peter Anghelides, Cybermark Services.