Category: Nix

The violet keystone by Garth Nix (Book 6 in The Seventh Tower series)

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.
A very good book, particularly the bit about the worm. K.A. (S3) ****