For eons, Earth has been under observation by the Firstborn, beings almost as old as the universe itself. The Firstborn are unknown to humankind—until they act. In an instant, Earth's timeline is carved up and reassembled into a patchwork of different eras, from prehistory to the year 2037, each with its own indigenous inhabitants.

Scattered across the planet are floating silver orbs impervious to all weapons and impossible to communicate with. Are these technologically advanced devices responsible for creating and sustaining the rifts in time? Are they cameras through which inscrutable alien eyes are watching? Or are they something stranger and more terrifying still?

The only clue lies in the ancient city of Babylon, where two groups of refugees from 2037—three cosmonauts and three UN peacekeepers—have detected strange radio signals. As the peacekeepers ally with nineteenth-century British troops and the armies of Alexander the Great, the cosmonauts join forces with the Mongol horde led by Genghis Khan. Both sides set out for Babylon, determined to win the race for knowledge—and the power that lies within.

Yet the real power is beyond human control, perhaps even human understanding. As two great armies face off before the gates of Babylon, it watches, waiting.