The confirmation of the King has been put on hold, and the Doctor works on repairing the android of the future king in time. Count Grendal meanwhile, having had his plans interrupted works to stop the confirmation so he can become king in the Princes place.

The Doctor and Romana land on the moon Delta III, home to the green-skinned Swampies and a small group of human colonists. Soon after arriving, Romana is taken by the Swampies who wish to sacrifice her to the mysterious squid-like Kroll.