When Kai's big sister Jen leaves the family home, Kai knows it's all his fault. His secret burns, but he tells no one, just keeps pulling at tufts of his hair. But in the broad branches of a wasteland sycamore tree, Kai feels safe and free from his worries. Up there he feels he can be whoever he wants to be. And when a girl called Sky starts climbing Kai's tree, a friendship blossoms ... a friendship with the power to heal.