Fen loves spending summers in Scotland with her grandfather. Among soaring mountain peaks, secret smugglers' caves, glittering lochs and wild waterfalls, there's always something new to explore. Equipped with the brilliant gadgets she invents herself, Fen is ready for any adventure.
But when she stumbles through a mysterious door hidden in the mountainside, she finds herself in a world beyond her wildest imagination.

Welcome to the Greenwild: a magical land where a colossal castle sits beneath the mountain, the orchards are full of living jewels, and magic sparkles out of every root, leaf and stem. But in this astonishing land, a mystery is afoot . . . and Fen might be the only one who can solve it.