Rue and Viri's new life as Moonruin Investigations is as peaceful as a monster hunter and a druid could hope for. Peaceful, that is, until the arrival of a bloodstained messenger in the middle of the night. She calls them to the rescue of a bard who claims to come from the fabled Summerlands, and who carries a request for help from an old ally.

Leaving home behind, the pair find an idyllic land under siege, watched over by none other than the Guardian of the Old Road. Except Merle speaks of imbalanced ley lines, whilst the very duke who aided Halamar is camped on the border. He's accompanied by an army of ghosts – and he has a decided interest in a mysterious tower that no one has ever been inside.

As new alliances are made and tested, bringing fresh revelations with them, both Rue and Viri must fight against the inherent flaws in their respective magics – and the Goldstone Tower looms over everything they do. If they can't unlock its secrets, both the Summerlands and the new peace they've made for themselves might well be lost forever.