The Doctor has encountered giant slugs many times in Doctor Who. But none more foul than the slimy, greedy Sil, a capitalistic creep from the planet Thoros-Beta. Sil and his race, the Mentors are exploitative creatures that thrive on the suffering of others. The Sixth Doctor and Peri encountered Sil twice onscreen, first on the prison planet Varos and later on Sil’s home planet of Thoros-Beta. These were meetings that the Doctor wishes that he could forget.

Vengeance on Varos

★★★★★

TX: 19/01/1985 – 26/01/1985

Written by Philip Martin    Directed by Ron Jones

The prison planet Varos is abundant in a rare mineral called Zeiton 7 ore. A despicable, slug-like alien creature called Sil is duping the Governor of Varos into believing that the element is almost worthless and that the prison planet’s only source of revenue is the commercial export of sadistic torture game shows within the punishment dome. The TARDIS stalls and the Doctor and Peri only have enough energy to reach Varos in order to refuel with Zeiton 7 ore, a power source for the TARDIS.

Peri is taken to the punishment dome with other prisoners and forced to be turned into a bird. The Doctor is able to escape and prove to the Governor of Varos that he is being fooled by the slimy Mentor Sil. The Doctor shows to the Governor that Zeiton 7 ore is valuable and that people all over the galaxy cry out for the product. This brings an end to Sil’s hold over the planet and to the sadistic entertainment that the decaying society on Varos was enjoying. It is very clear that elements of Vengeance on Varos were reused for Bad Wolf/The Parting of the Ways by writer Russell T Davies. Vengeance on Varos is one of a number of Doctor Who episodes that contains an anti-capitalist message, other examples include Oxygen and Boom. Capitalism is completely unfair and exploitative. The character of Sil is an allegory for corporate exploitation. The character of Lady Cassandra (“Moisturise me! Moisturise me!”) is partly inspired by the villain Sil from Vengeance on Varos and The Trial of a Time Lord: Mindwarp.

The Trial of a Time Lord: Mindwarp

★★★★☆

TX: 04/10/1986 – 25/10/1986

Written by Philip Martin    Directed by Ron Jones

As part of the evidence against him in his trial by the Time Lords, the Doctor is shown his most recent adventure before being taken to the courtroom. The Sixth Doctor and Peri arrive on the planet Thoros Beta where the natives are being experimented on by a scientist called Crozier. Crozier has been instructed to find a new body for the Lord Kiv, the leader of the slug-like Mentors. Events take a turn for the worst when the Doctor and Peri’s old enemy, Sil – another Mentor, arrives on the planet. The Doctor is experimented on and in the process his mind is negatively affected. Peri teams up with the warlord King Yrcanos and attempts to rescue the Doctor. However, the Doctor in his weakened mental state is now assisting Crozier and the Mentors. Peri is ultimately captured and her body is designated as the new host for Lord Kiv. Crozier performs the operation, transferring Kiv’s mind into Peri’s body, apparently killing her in the process. The Doctor, who has recovered his mental health, rushes to rescue Peri, but he is taken out of time by the Time Lords and brought to his court trial. Yrcanos enters the laboratory and discovers Kiv has taken over Peri’s body. Enraged, Yrcanos kills everyone in the room. Back at the trial, the court prosecutor, the Valeyard contends that the Doctor was responsible for Peri’s death due to his actions. However, the Doctor suggests that he was taken out of time for another reason, and that he has every intention of finding out what it is.