Why does the mysterious soldier march straight over a cliff - and then reappear unarmed?

Why are they attacked by the sinister mechanics with built in guns for hands?

Why is a picturesque country village at first deserted - then filled with mindless zombies?

And why are their best friends suddenly trying to kill them?

The Doctor has stumbled onto a cunning alien plan to take over the Earth. Will he be in time to defeat the deadly Kraals and their terrifying android invasion?
 

Doctor Who, that cocky, crazy, cosmic hobo, and his delightful companion, Sarah, land in the small English village of Devesham. The TARDIS has brought them safely home at last. Or has it? At first the picturesque village seems deserted, but then they discover zombie-like inhabitants who won't answer their questions, and a mysterious soldier who marches over a cliff and reappears without a scratch. And then there are the weird coffin-like meteorites that open up and contain human-like creatures. Have the body snatchers returned? What Doctor Who doesn't know is that the village is not English at all, nor is it on Earth. It's a replica on the polluted Planet Oseidon, the radiation-infested home of the Kraals. The few surviving Kraals must find a new home fast and are sending androids to Earth to take it over.

Will Doctor Who be able to outsmart his own android clone in a face-to-face battle of wits and stop the android invasion of Earth?
 

When the TARDIS materialises just outside a sleepy English village, it appears the Doctor and Sarah Jane are nearly "home" at last.

But all is not as it seems in rural paradise. White suited, gun weilding guards stalk the countryside, while the village itself is eerily deserted. As the Doctor and Sarah look on, a UNIT member leaps over a cliff to his death and, as the clock strikes twelve, the local pub is suddenly filled with strange robotic villagers. The UNIT member is amongst them, very much alive. What exactly is happening here?

The Doctor is mystified, setting off for UNIT HQ in search of the answers. There, with the Brigadier away, Senior Defence Astronaut Guy Crayford holds court. But just who is this shadowy master, the Thraal, Styggron? Indeed, who are the Thraals and what have they got in store for the Earth? Why has the TARDIS dematerialised seemingly of its own accord?

The Doctor must move quickly to find the truth, for the very future of mankind hangs in the balance ...

Originally transmitted 22 November - 13 December 1975, this four part story starring Tom Baker as the Doctor and Elizabeth Sladen as his assistant, was the last UNIT adventure for fourteen years, until "Battlefield" with Sylvester Mc Coy in 1989.

Running Time: 96 mins approx
Produced by Philip Hinchcliffe
Directed by Barry Letts
Cover Illustration by Colin Howard