Mindwarp is the second serial of the larger narrative known as The Trial of a Time Lord which encompasses the whole of the 23rd season of the British science fiction television series Doctor Who. It was first broadcast in four weekly parts on BBC1 from 4 to 25 October 1986. The title Mindwarp is not used on screen and appears only on the serial's scripts with the four episodes that comprise the story being transmitted as The Trial of a Time Lord Parts Five to Eight. This story marks the final appearance of Nicola Bryant as Peri Brown.

In the serial, the alien time traveller the Sixth Doctor (Colin Baker) is put on trial by his people, the Time Lords, and is accused of meddling in the affairs of the planet Thoros Beta in the 24th century. Much of the story consists of a video testimony presented by the prosecutor – the Valeyard (Michael Jayston) – of The Doctor discovering the alien arms dealer Sil (Nabil Shaban) is looking for a way to prolong the life of Lord Kiv (Christopher Ryan) by transplanting Kiv's mind into another.

The serial is presented as video evidence of a trial prosecuted by the Time Lord, the Valeyard, of the Sixth Doctor's interference into the affairs of other species.

As shown by the video, on Thoros Beta, Crozier, a scientist employed by the Doctor's old enemy, arms dealer Sil, is attempting to perfect the ability to transplant the mind of Kiv, Sil's superior, into another body to overcome Kiv's impending death. The Doctor and Peri are captured while investigating the planet, and the Doctor is tortured using a mind-altering device, before he and Peri are broken out by King Yrcanos, one of Crozier's test subjects.

With his mind apparently affected by the device, and the Doctor at the trial having minimal memory of events past this point, the Doctor suddenly betrays Peri and Yrcanos, who flee into the tunnels, and claims that he wants to work with Sil and the Mentors. Peri and Yrcanos, together with rebels from the neighbouring planet Thoros Alpha are captured. With Kiv's condition quickly deteriorating, the Doctor helps Crozier transplant Kiv's brain into the body of a deceased fisherman as a temporary solution, but complications in the procedure cause Crozier to realise the brain will not survive being transplanted again. Crozier instead suggests using his machine to transfer Kiv's consciousness into Peri's body directly. The Doctor frees Yrcanos and the rebels, and they destroy the device controlling the enslaved people from Thoros Alpha, throwing the complex into chaos right as Kiv's condition starts to deteriorate again.

While searching for Peri, the Doctor is drawn into his TARDIS, and the TARDIS is forcibly taken to the Doctor's trial by the Time Lords, which the Valeyard insists was to prevent the development of from further impacting the development of the universe. Kiv's mind is successfully transplanted into Peri, destroying her personality. Yrcanos, his entry into the lab delayed by the Time Lords until after Kiv awakens in Peri's body, is distraught at the results of the operation, and fires wildly, killing Peri.

At the trial, the Inquisitor insists that the interference of the Time Lords was to prevent Crozier from further impacting the course of the universe's evolution. The Valeyard says Peri's death was because the Doctor’s negligence made it "impossible for her to live". The Doctor insists that the present trial appears to be serving an ulterior motive, and resolves to determine what it is as the trial continues.

Initially it was intended that the BBC Radiophonic Workshop would provide music scores for both this and the following segment of The Trial of a Time Lord; both were assigned to Malcolm Clarke to begin with, although Terror of the Vervoids was reassigned to Elizabeth Parker shortly afterwards. However, fellow Radiophonic Workshop composer Jonathan Gibbs left early in 1986 and was not replaced until the following year, leaving the other composers backlogged and with no one free to do the incidental music for Mindwarp. It was suggested that Dick Mills could provide both the music and sound effects, but John Nathan-Turner rejected this idea and instead hired film composer Richard Hartley to create the incidental music for this segment. It would be the only time that Hartley worked on the series. The original recordings of Hartley's score no longer exist in the BBC archives with the result that there was no isolated score included on the DVD release of this story. For the Blu-ray release of Season 23, Richard Hartley, along with Mark Ayres re-recorded the entire score in order to present the serial in a new 5.1 mix.