When terrorists threaten to detonate a nuclear device outside RAF Lakenheath, Kelly Wells races for a nearby office block, frantic to find her sister in their last moments. At the same time, a handful of others do the same—all desperate to make it to loved ones before the bomb goes off barely fifty miles away. In the frozen second of the explosion, Kelly, her sister, and three strangers are trapped in that instant and trapped in the building. But they are not alone. A sleeping evil from the deepest pits of the earth has awoken. Stalked by a creature that knows their most private secrets and fears, the group are lost in a world of their individual Hells.