Botanica is an island, but almost all of the island is taken up by the Tree. Little knowing how they came to be here, small communities live around the coast line. The Tree provides them shelter, kindling, medicine—and a place of legends, for there are ghosts within the trees who snatch children and the dying. Lillah has come of age and is now ready to leave her community and walk the tree for five years, learning all Botanica has to teach her. Before setting off, Lillah is asked by the dying mother of a young boy to take him with her. In a country where a plague killed half the population, Morace will otherwise be killed in case he has the same disease. But can Lillah keep the boy's secret, or will she have to resort to breaking the oldest taboo on Botanica?