Book excerpt: Arthur Quinn has defeated the World Serpent. He's come face-to-face with the Fenris Wolf. But now he faces Loki's most powerful child, Hell's Keeper. With his friends Ash, Ellie and Ex, Arthur sets out to stop this new menace. But Loki has a trick up his sleeve, a trick that changes everything. Arthur must confront Loki for a final showdown. But faced with a terrible secret and enemies at every turn, can Arthur find the courage he needs to defeat the god once and for all, or has Loki finally won?