The TARDIS returns to London; however, it's the 22nd century. With bodies in the river, and quiet in the docklands, the city is a very different place. The Daleks have invaded and it's up to the Doctor to thwart them once again.

The Doctor, Ian and Barbara arrive on the planet Dido where a crashed spaceship with the only two survivors are terrorized by the monsterKoquillion. But who is Koquillion? But the enemy may be closer then they think...