After narrowly avoiding a terrible conflict, the humans and monsters of Seawaren have fallen into an uneasy truce. Sunny still hopes the monsters can be persuaded to help her community with the mysterious Goo they produce, which has the power to heal their poisoned crop fields. Mo is less sure, and his brother Blue – traumatised by his imprisonment by humans – remains openly hostile. But when Mo is kidnapped by a pair of wandering strangers and carried away, Sunny, Mo and their friends set off in pursuit. Their chase leads them through the Burnt Land to an impossible place beyond – the island of Pontyme, which is mysteriously free of poison. Here, monsters are revered as Divine Protectors, responsible for keeping Pontyme fertile and protected. But Sunny is suspicious of the island’s charismatic leader, Hadrian, and the power he seems to wield. While beneath the island, a shadow lurks, nursing a terrible thirst for revenge.