The twenty-third season of British science fiction television series Doctor Who, known collectively as The Trial of a Time Lord, aired in weekly episodes from 6 September to 6 December 1986.

It contained four adventures: The Mysterious Planet, Mindwarp, Terror of the Vervoids and The Ultimate Foe; the season also marked the final regular appearance of Colin Baker as the Sixth Doctor.

The idea for the serial stemmed from several production changes to Doctor Who, such as reduced screen time for the season and an instruction from BBC1 controller Michael Grade that the series needed to contain less violence and more humour.

This running time was the result of a plea by John Nathan-Turner to his superiors at the BBC that the serial's final episode needed the additional three minutes to conclude the story properly.

However, in the latter month, the BBC announced that, as a cost-cutting measure owing to the costs of several large projects (not least of which was the launch of EastEnders), Season 23 was being put back from its planned transmission in January 1986 to the following September, which would be a different financial year.

John Nathan-Turner and Eric Saward eventually came up with the idea of having the various serials linked with an overarching narrative—this led to the conception of a trial story with A Christmas Carol-inspired "past, present, and future" storyline,[1] thereby stretching the length of the season.

[15][citation needed] Holmes was unable to finish writing the fourth chapter, originally called Time Inc., before his death from a liver illness and Hepatitis B on 24 May 1986, aged 59.

[17] David J. Howe and Stephen James Walker, authors of Doctor Who: The Television Companion, disagreed, arguing that the serial was a 'monumental wasted opportunity'.

[18] They disapproved of the trial storyline, being unconvinced that a prosecutor 'in any reasonable legal system' would be allowed to modify charges and court proceedings mid-trial.

Although appreciative of the acting of Brian Blessed in Mindwarp, Cornell, Day and Topping argued that the script lacked focus, '[trying] to be comic, grotesque, straight, and farcical all at the same time'.

[23] Howe and Walker were more favourable towards the script, citing the re-appearance of Sil as positive, and hailing Peri's off-screen death as 'one of the most dramatic and impressive moments of the entire season' and Bryant's best scene since The Caves of Androzani.

[24] Both reviews judged Terror of the Vervoids to be a well-written story, although Cornell, Day and Topping criticised the dialogue, and Howe and Walker were unimpressed by Bonnie Langford in her performance as Melanie Bush.