Felix is not your usual hero. Though brave and intelligent, he suffers from a rare illness. His parents take him on the holiday of a lifetime to Costa Rica, where they visit the Continental Divide, the special point where the waters that feed into the Atlantic and the Pacific Oceans separate. There, Felix faints - and something extraordinary happens. He wakes up in an amazing back-to-front world where mythical creatures are real and humans are imaginary! Luckily, he's taken under the wing of Ironclaw, an enormous, maths-loving Brazzle, and Betony, a mischievous tangle-girl, who set out to help Felix find a magical cure and the way back home.