When the Tardis lands on an arid planet, it seems as though the whole place is desolate and lifeless. But then the Doctor, Steven, and Vicki discover two crashed spaceships: one contains the Drahvins, a race of stunning beauty; the other contains the hideous Rills. However, as the team soon finds out, appearances can be deceptive. It emerges that the beauty of the Drahvins hides a colony of mindless clones who are controlled by the cruel, powerful matriarch Maaga, whereas the ugly Rills are friendly and intelligent explorers.

The Rills tell the Doctor that the dried-up planet is about to die. Back in the control room of the TARDIS, he discovers they are right, but things are worse than they thought. There is only one day of life left...one day to escape.

With the Drahvins' ship damaged beyond repair, can the Rills get off the planet before the evil Maaga hijacks their craft in her own effort to escape?