Two years after the disappearance of the Nestene creature from UNIT's top-secret warehouse, it suddenly reappears, attacking again with Autons as its soldiers. Mysterious UNIT operative Lockwood investigates the Nestene's plan and is drawn to Sentinel Island, where the islanders are gripped by strange religious fervor. Lockwood teams up with Natasha Alexander, a new scientific advisor who has secrets of her own. To stop the Nestene, they must confront a powerful creature from humanity's distant past.