The Doctor and Ace visit England in 1988, where three rival factions - the Cybermen, a group of Nazis and a 17th Century sorceress named Lady Peinforte - are attempting to gain control of a statue made of a living metal, validium, that was created by Rassilon as the ultimate defence for Gallifrey.

The statue has three components - a bow, an arrow and the figure itself - that must be brought together in order for it to be activated. They have been separated since 1638 when, in order to foil the first attempt by Peinforte to seize it, the Doctor launched the figure into orbit in a powered asteroid.

This asteroid has been approaching the Earth at twenty-five yearly intervals ever since, leaving a succession of disasters in its wake, and has now crash-landed near Windsor Castle.

The Doctor plays the three factions off against one other and eventually appears to concede defeat to the Cyber Leader. However, this is just part of a carefully-laid trap, and the Cybermen's fleet is totally wiped out by the statue.