The search for the next segment of the Key to Time brings the TARDIS to one of the swamp moons of Delta Magna, which is populated by the hostile natives who are attempting to stop further encroachment on their lands with the aid of their god, Kroll.

This week Paddy and Tricia follow The Doctor and Romana as they attempt the find the penultimate piece of the Key to Time whilst trying to safe themselves from The Power of Kroll.