When a spaceship crash-lands outside of Rebecca Refractor's school full of aliens who look just like adorable hamsters, she knows there is only one kid and Superpet that can help - Jack and Hercules the hamster, the superstrength Superpet! The alien-hamsters can control minds and are determined to turn everyone on Earth into cracker-hunting zombies! But why are the aliens so cracker obsessed? And who (or what) is The Big Cheese - the villain boss the aliens serve?