This time the third segment of the Key to Time is hidden on Earth, and the trail leads the Doctor and Romana to an ancient Druidic circle, the Nine Travellers, where they come across Professor Rumford and Vivien Fay.
Research by Professor Rumford and Vivien Fay have shown that over the years the number of stones has varied. Looking for the third segment they meet a group of Druids, and the Doctor narrowly avoids becoming a sacrifice. The leader is later killed by an Orgi, a silicon based life form that must feed on blood.
The Doctor finds that the Cailleach, worshipped by the Druids, is in fact Vivien Fay, who had been living on Earth for 4,000 years. Before he can warn Romana she is taken up to Fay's spacecraft which is in hyperspace orbit. The Doctor follows and accidentally lets out the Megara.
The Megara are justice machines sent to judge Cessair of Diplos. Instead they nearly execute the Doctor, but during his trial he persuades them to look into the mind of Vivien Fay, and they discover that she is in fact Cessair of Diplos. They turn her into one of the stones in the circle, but not before the Doctor grabs her necklace, which is the third segment of the Key to Time.
