When the planet Archetryx is threatened by a Dalek assault squad, the Doctor and Evelyn become embroiled in an ever-deepening mystery. What has become of President Romana, missing for twenty years? What lurks in the vast gravity wells of Archetryx? What is the secret of the ancient element the Daleks are synthesising - and how does Gallifrey feature in the plans? The Doctor finds that if his oldest enemies cannot conquer the universe they will watch it go up in flames...