Parts: 4
Writer: Bob Baker
Airdates: 24 November 1979 - 15 December 1979
Production Code: 5K

Doctor: fourth
Companions: the second Romana, K-9 mark two

Creature Feature: Mandrels

Story: During a routine trip to the planet Azure, the starliner Empress goes off course and emerges from hyperspace directly in the path of another spacecraft. The two ships collide as the Empress materializes, fusing them together with considerably unstable matter interfaces. When the Doctor, Romana and K-9 arrive on board, the problem seems simple: just do a little clever thinking and manoeuvring, and get the two ships unstuck.

But, as always, the solution is not quite that easy. The reason why the ships are stuck in the first place is because the navigator was under the influence of vraxoin, an extremely dangerous and illegal drug. The only source was thought destroyed, but someone has found an alternate source...and a supply of vraxoin has been smuggled on board. Blissfully unaware of the danger, the navigator wanders into an unstable area of the ship...and is attacked and killed by some kind of creature lurking there.

Romana is suspicious that the problems may have something to do with the Continuous Event Transmitter, a machine brought on board by zoologist Tryst which stores planetary environments as electomagnetic signals in crystals. With the instability of the matter interfaces, the already-unstable CET is even less trustworthy. But with the Doctor and Romana being pursued by vrax smugglers, law enforcers who want them dead, and the deadly monsters hiding in the matter interfaces, can they split the ships apart and uncover the source of the vraxoin before it is again unleashed upon the universe?