The travellers meet the Drahvins, a predominantly female race. Their leader, Maaga, has a crashed spaceship and evil plans…
Intent on capturing the repaired spacecraft of the hideous Rills, Maaga holds Steven hostage and forces the Doctor and Vicki to go to the Rill ship.
The Doctor and Vicki learn the truth about the Drahvins from the ammonia breathing Rills. Meanwhile, when Steven attempts to escape the Drahvins, he finds himself in more peril.
As the planet faces destruction, Maaga launches a final attack on the Rill base. The Doctor offers to transfer power from the TARDIS to the Rill ship so that it might escape.