Paraworld Zero (Parallel Worlds)

Twelve-year-old earthling, Simon Kent, stumbles upon a secret that thrusts him into a bizarre adventure filled with magic, technology and deadly out-of-this-world creatures. He discovers a true friend, confronts his inner demons and becomes the savior to a peculiar race of people, when all he truly wants is to find his way back home. Parallel to Simon's adventures is a mystery involving a catlike spy and a magical swordsman who both struggle to maintain peace among the paraworlds. But evil lurks in unexpected places, and few people can be trusted. Their paths ultimately lead them to Simon: the one boy who might be able to prevent the biggest assassination attempt in the known paraverse.