In 2020, the most ambitious drilling project in history is under way. Dr Nasreen Chaudry and her team have reached 21 kilometers into the Earth's crust - but something is stirring far below. Amy Pond discovers there's nowhere to run when you can't even trust the ground at your feet.

It is the most important day in the history of Earth: the dawn of a new age of harmony… or the start of its final war. The Doctor must face his most difficult challenge yet and he tries desperately to ensure Alaya's prediction of a massacre does not come true. Meanwhile, what fate will befall the captured Amy and can Tony and his friends be trusted?