Dr Who and the Android Invasion

The Doctor and Sarah arrive safely back on Earth - or do they?Why does the mysterious soldier march straight over a cliff - and then reappear unharmed?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 on a cunning alien plan to take over the Earth. Will he be in time to defeat the deadly Kraals and their terrifying android invasion?