"The Forest King's Daughter" is the first book in a new young adult fantasy trilogy by bestselling author Blake Elly, known for her work "Frostblood." The story follows the fey princess Klara, who secretly sneaks out of her father's castle and forms a forbidden friendship with a demon boy named Zeru. During their third meeting, Zeru gives Klara a ring made of demon stone, which turns out to be a powerful and dangerous artifact. The return of the demons, who demand the ring back, leads to an escalating conflict between the demons and the fairies. Klara faces the challenge of proving herself and her worth, while Zeru, once her friend, is now an enemy seeking the opportunity to save his people. This captivating tale explores themes of friendship, loyalty, and the search for identity amidst an impending war.