The Violet Keystone (The Seventh Tower #6)

The sixth and final adventure in the thrilling fantasy series from award-winning author Garth Nix. Tal and Milla are only one step away from death, while the evil that has controlled their world for so long is about to triumph. If the Veil is lifted, nothing can save the Dark World. Their one glimmer of hope is to confront the monster Sharrakor and regain the Violet keystone. But first they must climb up to the highest levels and find their way into the Seventh Tower!