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 answer may lie in the ancient city of Babylon, where two groups of refugees from 2037 - three cosmonauts returning to Earth from the International Space Station, and three United Nations peacekeepers on a mission in Afghanistan - have detected radio signals: the only such signals on the planet, apart from their own. The peacekeepers find allies in nineteenth-century British troops and in the armies of Alexander the Great. The astronauts, crash-landed in the steppes of Asia, join forces with the Mongol horde led by Genghis Khan. The two sides set out for Babylon, each determined to win the race for knowledge...and the power that lies within.