At the bottom of a prehistoric lake in Antarctica there is a city old as time, a relic of an alien pre-human intelligence. Somewhere, deep in its ancient labyrinthine depths, there is an ever-increasing source of power of incalculable menace. Now an elite team of Navy divers is going down to investigate it, and what they find is a nightmare beyond imagining. The city is not dead. As it wakes from its deathless slumber of countless millions of years, so does the race that built it, unleashing a deadly force that will harvest the human race like cattle. Trapped beneath the ice, haunted by the city, its inhabitants, and the monsters spawned from their own fragile psyches, the divers have only one chance to destroy it before it rises to engulf the world of men. The clock is ticking. And the city's black heart is beating.