England, the 1820s. As the Industrial Revolution gathers pace, the village of Killingworth is disturbed by crazed Luddite miners intent on smashing all machinery and engineers. But is there another cause of the situation?

The Master uses The Rani's mind-controlling parasites to keep a meeting of Earth's leading scientists from being cancelled, and helps her plant transformation land mines for The Doctor, as he continues to propose an alliance with her in ruling over Earth.

The alien world of Lakertya. With the aid of the savage Tetraps, the Rani has conquered this planet to allow her to continue her depraved biochemical experiments. But she finds herself needing the Doctor's assistance...

The Rani's impersonation of Mel backfires badly because Urak can't tell the difference, while the Doctor attempts to learn the secret of the Loyhargil.

The solstice nears, making it time for the Rani to bring her plans into fruition. The Doctor's sympathies for Beyus, ruler of the Lykertyans, are rather qualified. Beyus' heart is for his people yet something prompts him to collaborate fully in helping the Rani reach all her objectives. The answer, he's told, lies within the Center of Leisure.

The Rani, at last, links the Doctor into her great brain machine, the crowning jewel in her component packet of geniuses brought together to turn Lakertya itself into one vast cerebral mass capable of redirecting time anywhere in the universe, giving her absolute power over all creation.