It all starts when Francesca and her best friend Isabella go on a picnic. Taking shelter from a storm, they stumble into the strange Inside World, where they meet the Nibby Nabbies, the evil Crone Koniferous, the wizard Metzler and countless ravenous monsters. It is down to the girls' ingenuity and courage to find a way back home, dodging pirates on the way.

And then the witches get in on the act.