Stephen Baxter

Returned to the Earth of 2037 by the mysterious and powerful Firstborn, Bisesa Dutt is haunted by memories of her five years spent on the strange alternate Earth called Mir, a jigsaw-puzzle world made up of lands and people cut out of different eras of Earth's history. Why did the Firstborn create Mir? Why was Bisesa taken there and then brought back just a day after her disappearance?

Failing to eliminate life on Earth after their first attack, the Firstborn send a Q-bomb weapon to finish the job. Two cryogenically frozen females and a group of scientists studying the Eye, an artifact of the Firstborn, may be the only hope of finding a way to counter the onslaught.