The Ribos Operation

From: http://www.bbc.co.uk/doctorwho/classic/episodeguide

The White Guardian gives the Doctor a quest to find the six disguised segments of the Key to Time which, when assembled, will be used to restore the balance of the cosmos. To aid him he is given a new companion, a female Time Lord called Romana, and a tracer device.

He tracks the first segment to the city of Shur on the planet Ribos. There con men Garron and Unstoffe are engaged in a scam to sell the entire planet to the Graff Vynda-K, deposed ruler of Levithia. The Graff has been tricked into believing that Ribos is a rich source of jethrik, a rare mineral vital for achieving space warp drive.

His interest is further piqued when he sees a large lump of the mineral on display in a reliquary. The Doctor realises that this is actually the first segment but, before he can steal it, Unstoffe spirits it away.

The Graff, having discovered the trick that has been played on him, hunts the con men down and captures them, along with the time travellers, in the catacombs beneath the city. He is on the point of having them executed when Riban guards blow up the entrance to the catacombs.

The death of his loyal officer Sholakh in the ensuing rock fall unhinges the Graff's mind. He storms into the dust and is killed by a thermite bomb with which he had intended to destroy the catacombs.

The Doctor, Romana and K9 depart with the jethrik, leaving Garron and Unstoffe to make off with the Graff's ship of plundered loot.

1 out of 96 (1.0%) raters say this story requires a previous story.