Therefore, its known narrative elements are not a part of the Doctor Who universe as we, on this Wiki, choose to define it. It may have been the basis for a similar story in another medium, however — and that story may indeed be valid.
Attack from the Mind was an unproduced story by David Halliwell. It was to have been the third segment of The Trial of a Time Lord.
At the Doctor's trial for meddling, the Valeyard presents evidence from the future to show that the Doctor will not learn the error of his ways. The TARDIS is lured to the planet Fred, where tunnels are being excavated by the rodent-like natives who are plagued by vivid mirages. The Doctor and Mel are captured by the Freds, but the Doctor is freed by the lemurine Penelopeans, beings who now dwell within their own imagination. The Freds are hunting for their control centre to prevent them from returning to corporeal form; the hallucinations are the Penelopeans' defence system. The Doctor agrees to bring a Fred back in time so that the Penelopeans can devise a form of protection against them. However, he is recaptured by the Freds, who complete their excavation. In fact, the Penelopeans are homicidal beings who retreated into their own minds so that they would not wipe themselves out. They have been toying with the Freds -- a peaceful race -- out of boredom. The Doctor and Mel escape to the TARDIS as war breaks out between the Penelopeans and the Freds. The Valeyard explains that the intervention of the High Council would be required to deal with the consequences of the Doctor's meddling.
David Halliwell was part of the original writing team for what would become The Trial of a Time Lord. He and Jack Trevor Story were asked to develop the "future" element of the evidence against the Doctor. These would be two linked two-part adventures, which would share most of their sets (as had also been done in Season 12 with The Ark in Space and Revenge of the Cybermen). Halliwell's story would introduce new companion Melanie Bush. After an initial meeting of the writers with script editor Eric Saward on 9 July 1985, Halliwell quickly set to work; Saward accorded his segment the title Attack From The Mind in mid-August. In mid-September, Saward requested various changes to the scripts. The planet Fred (which stood for FRee Equal Democracy, with Penelope an acronym for PENultimate ELegance Order and PoisE) would now be planet Trike, and the Trikes would not speak with the East End accents Halliwell had intended. Conflict would be generated amongst the Trikes by dividing them into a militaristic camp and visionary camps. Several elements were excised, such as the Doctor being willing to use the TARDIS to change history, he and Mel being miniaturised by the Penelopeans, and the Doctor shooting his enemies dead. The story would now end with the Penelopeans losing their powers and the Trikes in control, to segue into Story's The Second Coming. However, Story was struggling mightily, and Saward found Attack From The Mind listless. Consequently, after five drafts, Halliwell's scripts were abandoned on 18 October. (REF: DWM 201, DWMSE 3)