InterWorld

A lad discovers that he can walk between alternate Earths—and is swept up in a war between them in this fast-paced, compulsively readable tale. Joey gets lost in his own house, but when he steps into a patch of fog and finds himself in a world where he died, a trillion Earths lie open to him—arranged in a vast arc, with an empire of science-based planes at one end and a realm where magic rules at the other. Recruited into an army of anything-but-identical Joeys gathered from many of these worlds