State of Decay

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

The Doctor, Romana, K9 and Adric - an Outler from Alzarius who has stowed away aboard the TARDIS - arrive on a planet where the native villagers live in fear of 'the Wasting' and of three Lords named Zargo, Camilla and Aukon who rule from an imposing Tower. The Lords are soon revealed to be vampire servants of the last of the Great Vampires, a race referred to in Time Lord mythology.

The Great Vampire is about to be revived from its resting place beneath the Tower - in fact the spaceship in which the Lords, in their original human forms, came to E-Space - but the Doctor launches one of the ship's three shuttle craft and it pierces the heart of the creature, killing it. The Lords, deprived of their master, crumble to dust.

53 out of 90 (58.9%) raters say this story requires a previous story.