Little Billy escapes his over protective mother to explore the world beyond the garden gate, where The Forest of Sin lies. When Billy strays into the forest, he meets the Minpins - tiny people who live within the hollow trees. The Minpins tell Billy about the Red-Hot-Smoke-Belching Gruncher, who preys on them. Billy embarks on a mission to rid the Minpins of their foe once and for all, and sets off - on the back of a swan - to confront The Gruncher.