Maryellen is in charge of planning her tenth birthday, designing a flying machine, and - most important of all - taking care of the family dog, Scooter, on a camping trip. One night, while she's holding down the fort, Scooter disappears. Maryellen is desperate to find him before the others return, so she and her bossy big sister, Joan, set off to search the woods. Suddenly, Joan disappears. Now Maryellen's really in charge, whether she wants to be or not! Can she find Scooter, rescue her sister, and figure out how to make something fly - all in one night?