Interworld Paperback Neil Gaiman.   Joey harker isn't a hero in fact he's the kind of guy who gets lost in his own house. But one day, Joey gets really lost he walks straight out of his world and into another dimension.  Joey's walk between worlds makes him pray to armies of magic and science both determined to harness joey's power to travel between the dimensions.  The only thing standing in their way is Joey or more precisely an army of joey's all from different dimensions and all determined to save the world's.  Now Joey must make a choice return to the life he knows or join the battle to the end.