Doctor Who: The Ultimate Foe (1986)

Charged with genocide by the treacherous Valeyard at his trial, the Doctor receives help from an unlikely source to turn the tide of the High Council's rulings in his favour and reveal the Valeyard as a wrongdoer: the Master. For the Valeyard's own crimes are so atrocious, even the Doctor's archenemy will help him to ensure that the villain won't see the light of day again. Cornered, the Valeyard flees to the Matrix, where he can be the Doctor's judge, jury and executioner...