Alien in my pocket. bk.8, Space invaders

Zack has grown fond of his troublesome buddy, Amp, since the four-inch-tall alien crash-landed his spaceship through Zack s bedroom window. They ve gotten into more than their fair share of trouble together, but they ve always invented a way out of it. Until a fleet of ships from Amp s home planet filled the sky and started firing its weapons. Zack and Amp have to do the thing most kids only dare imagine save the world!