There's an alien in my underwear! - Bruce Coville

When Tim Tompkins comes home and finds a two foot high orange alien called Beebo Frimbat sitting at his desk, he knows he's in for a hard time. After all, Beebo is a dedicated mischief-maker who thinks trouble is the spice of life. But even Beebo's past pranks don't prepare Tim for finding his underwear flying from a school flagpole.

Still, it's all in fun. Or is it? Do Beebo's pranks have anything to do with the plan to derail the mission of the Fatherly One? And is it really just an accident when Beebo locks Pleskit's faithful bodyguard into an alternate dimension populated by man-eating monsters?