Cirrus@Austlit

'When Bernice Summerfield visits the People -- an incredibly advanced civilisation living in a Dyson Sphere -- she discovers that even in utopia they still have their problems.

An illegal time travel experiment threatens a war which could destroy them all. Rather than risk it, the People and their ultra-powerful computer, God, are prepared to eradicate the source of the problem -- the ancient city of Babylon. But such action would involve the death of a quarter of a million human beings, and do incalculable damage to Earth's history.

Babylon -- and the human race -- have one hope. Benny returns to the cradle of civilisation to try and stop the interference. She has just one week to prevent a catastrophe that could mean she will never be born. Her only assistance comes from a Victorian linguist who has stumbled across the experiment himself. But he's no help at all -- even though he has a power neither of them suspects.'

Source: Doctor Who Guide (http://www.drwhoguide.com/who_na71.htm). Sighted: 4/8/2011