"Those who are intelligent, strong and virtuous are promoted. The stupid, the weak and the unworthy will die. How else is it possible for the world to make progress?"

The TARDIS lands on Nooma, a world in the middle of an industrial revolution. But the Third Doctor, Jo and Mike Yates quickly discover that there is no limit to the upheaval. The sky is alive, and at war with the ground. The continents are on the move, competing for a place under the sun. And somewhere, there is a starship...

Mike finds himself committed to a fight where his only option is to kill or be killed. Jo is caught in a workers' revolt. And the Doctor must find out what is really happening to Nooma before the struggle for survival kills the world and everyone on it.