Daisy Thistledown has escaped from boarding school and has a mystery to solve. Her search for her missing mother will lead her across London and through a hidden doorway to another world, filled with plants and bursting with magic: the Greenwild.

But all is not well in this astonishing land. Before long Daisy finds herself confronting a dangerous presence that threatens green magic on both sides of the door. Daisy must band together with a botanical genius, a boy who can talk to animals, and a cat with an attitude, to channel the power that can revive the Greenwild and find her missing mother - and save her own world too.