It had to be somewhere, Carmody knew that much. It was waiting for him, just as he had left it. But where? He only knew he was in the center of a galaxy in a universe of galaxies. Within them lay endless varieties of the planet Earth. And there was only one way to find his Earth again: he would have to visit each one. And he would have to hurry--because his search for home had turned into a race with death.

(From Goodreads)