As further evidence against the Doctor, the Valeyard reveals another example of the Doctors meddling. This time, the Doctor and Peri are visiting Thoros Beta, the home world of Sil; a creature they previously met. (Vengeance on Varos) Last time, Sil turned Peri into a half-bird creature. The Doctor is on the planet investigating how a warrior race acquired advanced technology. But it isn't long before they are captured and identified by Sil.
As the Doctor is being interrogated, he's rescued when another prisoner, (King Yrcanos; played by Brian Blessed) escapes and wrecks havoc in the science lab. He frees the Doctor and all three escape. They then run into Dorf, Yrcanos' companion, who has been experimented on by the mad scientist Crozier. He's now more of a dog/wolf-like creature.
With his swiss-cheesed brain, the Doctor is having problem remembering events the way the matrix is showing the rest of the court room. So he's surprised to watch himself betray both King Yrcanos and Peri. King Yrcanos swears vengeance on the treacherous Doctor, who has now sided with Sil and Crozier. Crozier's aim is to remove the mind of the dying leader Kiv, to that of another body. The Doctor announces to the court, though he can't remember, it was likely a ploy to discover more information.
King Yrcanos soon gets his chance to avenge himself on the Doctor but is thwarted by Peri, who refuses to see the Doctor die. She's uncertain of why the Doctor turned on them, but knows he's a good guy. Yrcanos is confused, but soon forgives Peri when he discovers an underground movement to rebel against Kiv and Sil. Yrcanos believes it will be a glorious fight, but they are soon captured.
The mind transplant is successful, to some degree. It works, but has to be perfected. Crozier is determined to try one more time, under pain of death (or so decreed by Kiv). When Crozier makes it know he wishes to use Peri, the Doctor is given the option of finding a better candidate. As the Doctor heads off to a slave conversion room, Crozier orders Peri brought to him anyway, unbeknownst to the Doctor.
The Doctor next goes to release the King Yrcanos and the rest, but Peri is already gone. Though he has sworn to kill the Doctor, Yrcanos agrees to let the Doctor live and accept his help. As the fighting commences, Dorf is killed in battle. Making their way to free Peri, the Doctor is suddenly drawn out of time and space by the Time Lords, which is how he appeared at the beginning of the first Trial Story. The Doctor demands to know why they pulled him out of space and time at such a crucial time.
This time the Inquisitor informs the Doctor of the reason. The High Council of the Time Lords felt things had gotten out of hand and that Croziers experiments could alter the balance of the universe. Having frozen King Yrcanos in time temporarily, the Doctor is shocked to learn the Time Lords are using him as an executioner. But the biggest shock of all is when the Doctor sees Crozier has successfully implanted Kiv's mind into that of Peri. The Time Lords then release King Yrcanos who goes on to exterminate everyone in the room, including Peri (Whom ). The Doctor refuses to believe it, but knows the Matrix can not lie.
WHO: Perpugilliam Brown
DEPARTURE LOCATION: Thoros Beta, 2379
REASON FOR DEPARTURE: Assassinated by King Yrcanos after the mind of Kiv had been superimposed onto her mind.