Aired 13 years ago - May 22, 2010
Location: Cwmtaff, Wales Date: 2020 Enemies: Silurians 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.
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