Missing--One Brain! - Bruce Coville

Pleskit loses his grandfather's brain in this third book of the hilarious, fast-paced, and accessible Sixth-Grade Alien sci-fi series from the bestselling author of Aliens Ate My Homework, Bruce Coville.
Some kids lose their homework. Some kids lose their math book, or their sneakers, or their lunch. Pleskit Meenom, first alien kid to go to school on Earth, has a bigger problem: He's lost his grandfather's brain!

Of course, that's not Pleskit's only problem. He's also feuding with his best friend, Tim. And someone is leaking stories about him to the press. Sixth grade is turning out to be an even bigger challenge than interplanetary navigation.

But if Pleskit can't find that missing brain, none of those other problems will matter. Because how do you explain that you've lost your grandfather? And Pleskit may not be the only one looking for him...