The one where Peri gets a new haircut, Brian Blessed yells at everyone, and the Doctor apparently sells out his best friend for reasons even he doesn’t understand.
Short Synopsis
The Doctor and Peri land on Thoros Beta, home of dodgy brain experiments and even dodgier costumes. The Doctor gets suspiciously cozy with the villains, Peri gets her brain hijacked, and the audience gets one of the bleakest companion exits in Who history.
Extended Storyline
We’re still in the courtroom, folks, where the Valeyard queues up Exhibit B of “Why the Doctor Is a Menace to Society.” This time, it’s his little trip to Thoros Beta, which is about as relaxing as a week in Chernobyl.
The Doctor and Peri arrive to find Mentor scientists experimenting with brain transference — because if there’s one thing Doctor Who loves, it’s villains poking around in people’s skulls. Their leader is Sil, the slimy, money-obsessed amphibian who first popped up in Vengeance on Varos. He’s still slimy, still obsessed with profits, and still has a laugh that makes you want to invest in earplugs. His boss, Kiv, has a brain that’s expanding faster than a bad balloon animal, so the plan is to stick his mind into someone else’s body. Naturally, Peri ends up top of the donor list.
The Doctor starts poking around, makes a few enemies, and then — shocker — suddenly seems to side with the bad guys. He laughs maniacally, rats out Peri, and generally acts like he’s been body-snatched, brainwashed, or just plain written inconsistently. The trial narrative insists it’s genuine treachery, but even the audience can tell something’s off.
Enter Yrcanos, played by Brian Blessed at his Brian Blessed-iest. He’s a warrior king who bellows every line as though he’s trying to communicate with Mars. Subtlety? Never heard of it. He’s leading a ragtag rebellion against the Mentors and quickly adopts Peri as his “warrior queen.” (Peri is less thrilled about the shouting, more thrilled she might finally get a storyline.)
The story flips between the Doctor playing court jester for Sil, Peri trying to keep her head attached to her body, and Yrcanos charging into rooms like a caffeinated rhino. Meanwhile, Kiv’s condition worsens, and the Mentors get serious about brain-swapping. The Doctor eventually tries to put things right — but it’s too late.
In the most infamous moment of the entire season, Peri’s brain is forcibly replaced with Kiv’s. She dies on-screen, screaming, while Yrcanos charges in a moment too late. Even the courtroom is shaken: the Valeyard smugly points out this is what happens when the Doctor meddles, while the Inquisitor looks like she’s reconsidering her entire career. The Doctor himself is horrified… until the Time Lords reveal that they plucked him out of the timeline before the final events, leaving him clueless. Convenient.
The story ends with Peri apparently dead, Yrcanos mid-battle rage, and the trial audience (and the real-life audience) left reeling. And that’s how Mindwarp cemented itself as the Sixth Doctor’s darkest hour.