What if the cataclysmic Tunguska explosion of 1908 was caused, not by a meteor or a comet, but by a microscopic black hole? What if that fantastic object - smaller than an atom, older than the stars, heavier than a mountain - is still down there, orbiting deep inside the earth, slowly consuming the planet? What if only a rookie government agent and an uncannily-insightful consultant stand between a renegade Russian billionaire and his plans to use the black hole to change history - or end it ...