When a wombat knocks on her window one night, Josie hopes her lifelong wish for a pet has come true. But Ursula the wombat is on an important mission for the Fellowship of Underground Nocturnals (the FUN). The FUN need human-help to solve their wildlife woes. After proving how well they work as a team, Josie and Ursula are invited to join the FUN's MEGA Division, which will make them mega-sized. But will joining the MEGA Division be a mega mistake?