Nightmare of Eden

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

The TARDIS arrives on the space liner Empress which has become locked together with a private ship, the Hecate, after colliding with it on emerging from hyperspace.

The Doctor and Romana meet the scientist Tryst, who has with him a Continuous Event Transmuter (CET) machine containing crystals on which are stored supposed recordings of planets that he and his team have visited.

Someone on board the liner is smuggling the dangerously addictive drug vraxoin, and to complicate matters the interface between the two ships allows some monstrous Mandrels from the mud-swamps of Eden to escape from the CET machine - which does not merely take recordings but actually displaces whole planetary areas into its crystals.

The smugglers are revealed to be Tryst and the Hecate's pilot, Dymond. Vraxoin is in fact the material into which the Mandrels decompose when they are killed. The Doctor thwarts this plan, separates the two ships and returns the Mandrels to Eden.

2 out of 79 (2.5%) raters say this story requires a previous story.