A large number of children have been leaving school for suspicious reasons, and Henrietta is convinced she knows who’s behind it. When her best friend Lina disappears, Henrietta follows the kidnapper onto the roof, into the school greenhouse, and to a whole new world - where pigs grow on trees, giant bees lurk beneath the ground, and the people have enormous goat-like horns.She makes friends with a grumpy Tree Pig called Dagenham, and a human who claims to be the world’s greatest d...