The World of the Unknowns: The Rescue.
by Nadia Bethell
After escaping from the World of the Unknowns, Bradley and Megan find out they have not been missed at home. What is worse, they have somehow acquired a rotten reputation both at home and at school. While trying to regain the trust of their parents and teachers, the children figure out who has acted on their part while they’ve been gone and design plans to rescue others from the Unknowns.