The longest 'Doctor Who' story ever. The Doctor (Colin Baker) is put on trial by his people the Time Lords for interference in the affairs of others; three segments of his past and future are presented as evidence. 'The Mysterious Planet' shows the Doctor and Peri (Nicola Bryant) in a battle with a megalomaniac machine on the planet Ravalox, but what are the mysterious 'secrets' it protects? 'Mindwarp' shows the Doctor apparently betraying Peri to the vile Sil (Nabil Shaban) and the Mentors - can the Matrix be falsifying the evidence against the Doctor? In his defence he presents 'Terror of the Vervoids', a future story where the Earth is threatened by evil plant life forms. In the final two episodes, 'The Ultimate Foe', the Doctor learns the truth about his prosecuting counsel, the Valeyard (Michael Jayston), and has to enter the Matrix to battle for his remaining lives. This was Colin Baker's last story as the Doctor.