"Today, prudence shall be our watchword. Tomorrow, I SHALL SOAK THE LAND IN BLOOD!"The trial continues, and the Valeyard decides to bring out another piece of evidence against the Doctor: his antics on the planet of Thoros Beta.The footage shown to go along with the trial has the Doctor and Peri landing on the aforementioned Thoros Beta, a planet beach with green sky, blue rocks and a pink ocean. They meander around the beach before going into a cave - and are quickly captured by natives of the planet. Among those aliens is Sil, whom the Doctor suspects is behind the problems of this planet as well. As it turns out, this is Sil's homeworld, the planet of his species: the Mentors. The Doctor and Peri are taken to a Doctor Crozier and his experiments - one of them being the ever-lovable BRI... King Yrcanos. Before the Doctor can object, a lie detector is slapped on his head and the Mentors begin to probe his mind. Before it can do much, however, Yrcanos blows up the machine, breaking free and taking the Doctor and Peri with him. Yrcanos plans to go steal weaponry and blow up the Mentors, but the Doctor then whacks the king on the head and turns Yrcanos and Peri over to the Mentors.As it turns out, the Mentors are being evolved into higher beings by Doctor Crosier - and the leader Kiv now needs a new body before his brain essentially explodes. Trying to avoid himself becoming a target of that transplant, the Doctor interrogates Peri and accuses her of being against the Mentors repeatedly. Meanwhile, the Doctor is denying that this happened at all during the trial - and that he's being manipulated by someone who's messing with the Matrix (again, not that one). Finally, Yrcanos escapes with Peri and both join the resistance against the Mentors - and plan a massive attack against the Mentors as well, but are stunned and captured. Sil and Crozier decide to use Peri as a more suitable body for Kiv's brain, despite the Doctor's objections. As the operation is being prepared, the Doctor sneaks away and frees Yrcanos, urging him on for Peri's safety.Peri is strapped down and gagged as the operation is prepared. As the Doctor and Yrcanos run to go save her, the Time Lords intervene and rip the Doctor out of time... and then purposely delay Yrcanos' strike force from actually freeing Peri until after the experiment is over with. As you can guess, the Doctor (finally remembering the events of this story, piece by piece) is not pleased with this at all.Time slowly resumes its normal course and Peri is now long since gone - replaced in her own body by Kiv. Yrcanos, having fallen for her over the course of the story, is devastated and blows everything up - whatever remains of Peri included. The Doctor, watching this from the courtroom, is shocked into silence. Rather than numbly accept the accusations of the Valeyard, however, the Doctor simply vows to get to the bottom of all this, and that he will somehow avenge the loss of Peri.
This serial is most notable for featuring venerated actor BRIAN BLESSED in a major role as King Yrcanos. This serial is more notable among the fans, though, for having a companion killed off rather than given a happy ending... at least until Executive Meddling went about and reversed it at the end of the season.
- Alien Sea and Alien Sky: Thoros Beta has a green sky (with another planet visible, large and close enough to see its rings) and a pink ocean.
- Author Appeal: The concept of the Mentors being a heavily-capitalist society, buying up planets and then using them up is a self-admitted example from author Philip Martin. No one really cares, though, because the whole effect of the species is just that cool - especially for the 1980s.
- The Bad Guy Wins: Although it gets reversed in the end, Peri's death ends up casting the Doctor in an even worse light than before.
- Bald Women: Peri, after the surgery placing Kiv's brain in her body.
- Big "NO!": King Yrcanos (BRIAN BLESSED!), who else?
- Crapsack World: Thoros Beta.
- Distressed Dude: Damn, Yrcanos just can't stay free.
- Dropped a Bridge on Him: Subverted; Peri's character's death was overturned in "The Ultimate Foe".
- Grand Theft Me: Poor, poor Peri.
- Ham-to-Ham Combat:
- BRIAN BLESSED, Colin Baker, the entire damned cast... BRIAN is the unquestioned winner, though; even the Sixth Doctor is eventually left stunned in the awesome face of King Yrcanos' loudly delivered calls to battle. Let that sink in for a moment.
- Horribly averted by Tusa, though. His actor recites his lines in a way that can't really be called "acting".
- Heroic BSOD: Played straight with the Doctor at the end of the serial. Subverted with King Yrcanos, as he suffers from one... but that ends with the typical results of a Villainous Breakdown instead.
- Mad Doctor: Crozier.
- Mind Screw: Exactly how "real" the events of this story are is never stated.
- La Résistance: Yrcanos and his merry men.
- Plot Hole: The Doctor's behavior during the flashback footage after Yrcanos frees him from the mind-machine. Supposedly, the Doctor was supposed to be blended with Yrcanos' personality — but a serious communications problem prevented Colin Baker from getting this important piece of information. As such, the Doctor comes off as a royal jerkass. Baker explains the script problem in this interview.Colin Baker: He said "I don't know, you'd better ask Philip Martin", so I got in touch and gave him those three alternatives, he said "I don't know, Eric wrote the trial stuff, all the Matrix stuff was added after, by Eric, you'd better ask him." So I went to John Nathan-Turner, he said "Oh, whichever you like."
- Shout-Out: When first in Crozier's lab, the Doctor examines a chestburster in a glass tube.
- Special Effects Beef Up: Just... damn. The scenery has been turned into something fantastic with just a subtle application of a retro software known as Quantel Paintbox. Think of it as a 1980's Photoshop for film.
- Unreliable Narrator: The Matrix itself, here. The Inquisitor says otherwise.
- Was Once a Man: The Lukoser. Now he's a sort of horrifying mutant man-wolf hybrid, though his mind is still clear enough to fight for Yrcanos.
- What the Hell, Hero?:
- The Doctor is called on his Moral Dissonance behavior by Peri, who is just as confused as the audience as to what the hell is going on.
- The Doctor also calls out the Time Lords on their intervention in Peri's rescue.
- World of Ham: Perhaps one of the hammiest productions Doctor Who has ever done.