The Doctor takes Romana down to investigate the planets mines and gets unexpected help when the Captains guards show up to confront them.

In their search for the 3rd segment of the key to time, the Doctor and Romana land on Earth at a Stonehenge type site where worshipers are engaged in their practice and people are being killed by unknown causes. While en route the Doctor and Romana hear a strange voice that says 'Beware the Black Guardian".