The Tenth Planet is probably the most notorious of all the missing Doctor Who stories. Three of the episodes - the first three - are still held by the BBC Archives. Part 4 was never officially junked, and rumours abound of its existence. The fact remains, though, that the episode has been missing since 'Blue Peter' showed a brief clip from the episode in 1974; after over twenty years, the chances of ever recovering the last episode are slim.

Part 4 of the story is sought after for two reasons. Firstly, as the only missing episode of the story, its recovery would allow the BBC to release the complete story on video; secondly [SPOILERS!!! If you do not know the ending of this story, SKIP THE REST OF THIS PARAGRAPH!] it marks the final moments of William Hartnell's tenure as the Doctor, and features the series' first regeneration scene. While we now take regenerations for granted, the audience of 1966 would have been shocked by the final moments of the story.

[SPOILERS OVER!]

As the first three episodes of the story do still exist, and are available on video in fan circles, we only currently have episode 4 transcribed into script form. The story of the first three episodes is as follows...

The Doctor, Ben and Polly arrive at International Space Command's tracking base in the Antarctic, in December 1986. They are arrested and brought into the base, which is currently monitoring a new planet headed towards the Earth. The Doctor notices that the new world seems to be a mirror image of Earth - almost as if it were a twin planet.

ISC have sent a rocket ship to investigate the new planet, but as it approaches it experiences a total power failure, and plummets out of control. A second ship - codenamed Zeus 5 - is sent on a rescue mission; the pilot is Terry Cutler, the son of the South Pole base's commander, General Cutler.

The 'Tenth Planet' turns out to be inhabited... the base is invaded by strange humanoid creatures covered in silver suits, with large units over their chests, torch-like helmets and deadly weapons - the first Cybermen! The Cybermen overrun the base, and explain that their home planet - Mondas - used to be Earth's twin. Millions of years ago, it was flung out of the solar system on a long orbit, and has only now returned. The humans who once inhabited Mondas have converted themselves using Cybernetics - their bodies are now machines, and their brains are devoid of any emotions.

The Cybermen invasion is repelled, but Mondas still approaches. It appears to draw energy from the Earth - and Terry Cutler's rescue craft. General Cutler orders the priming of the Z-bomb, a lethal rocket which will split Mondas in half. His chief scientist, Barclay, and Dyson warn that the nuclear device is likely also to destroy Earth, and Barclay sends Ben to sabotage the rocket. The Doctor, who has been strangely subdued throughout these events, collapses and is taken to rest. Meanwhile, a second Cyberman ship lands near the base. Cutler panics and orders the launch of the rocket; he discovers Ben in his sabotage attempt, and knocks him out with a blow to the head.

As Ben recovers in the main Tracking Room, he is unable to remember whether his sabotage attempt was successful. The Cybermen approach the base, and the countdown to the launch commences...