The Doctor's TARDIS materialises on a medieval-style planet in E-Space. The townsfolk live in fear of the Three Who Rule, who govern from their mighty castle. Investigating, the Fourth Doctor discovers that the Three Who Rule are ancient astronauts who became vampires long ago, and their castle is actually their spaceship.

When companions Romana and Adric are kidnapped, the Doctor must ally himself with a band of renegade peasants to stop the resurrection of one of Gallifrey's greatest enemies: the King Vampire itself.

State of Decay was a direct-to-cassette version of the televised story of the same name. It was distinct from both the TV story and the Target print novelisation. With a runtime of a mere 60 minutes, and a more or less in-character reading by Tom Baker, it had a very different format to the other two versions of this story.

It was one of the very few pieces of Doctor Who merchandise that was released on 1/4" audio cassette