The planet Spiridon, the year 2540. The Doctor and Jo arrive on the trail of the Daleks, and find unexpected allies in the shape of a Thal suicide squad. But what has brought the Daleks here in the first place?

The Doctor is captured by the Daleks, while Jo is rescued by a friendly Spridon named Wester.

The Doctor and his friends prepare to refreeze the Dalek army but the Dalek Supreme has arrived on the planet determined to destroy them all.