As the Underground is under siege by the Vaun siblings, Autumn and Luke Oaken juggle newfound problems that come with royal elves turning eighteen. The age-old question, "Who will be the next heir?" forces a divide between the twins. On top of the most important decision of their lives, they must join the rest of the Warriors as they fight to keep Arbor Falls safe. But after a deadly attack within their walls, the twins and the rest of the Quinns...