In a mystical land, the "wise beyond her years" Princess Allise finds herself trapped in Castle Locksley and promised in marriage to King Rubert as part of a political alliance. When she discovers a half-brother, eight-year-old Bertram, she learns the dark truths of her father, King Ewing, and his illegitimate children. Allise and Bertram spend their days roaming the castle through hidden passages, and when they discover the king's treasure, they gradually steal from it over time. They also discover their healing powers and learn the uses of potions and medicines.
Allise vows never to marry King Rubert, and for several years she plots her escape. Before she turns sixteen, King Ewing tightens security around Allise, yet she and Bertram strategically carry out their plan and go into hiding. As King Ewing searches for his daughter, Allise and Bertram live and work among villages as commoners. Yet their journey is not without dangers, and though Allise outwits her father at every turn, she knows she must face him once more.
With a sprawling cast of rotating characters in a story that shifts over time, Simmering offers a tale filled with heroes and villains, battles, strange creatures, and magic. The novel's high point is its principal characters, Allise and Bertram. The royal siblings' compassion and healing powers used for good among all the darkness surrounding them is refreshing. Simmering aptly employs all the requisite tropes of a fantasy adventure novel. At times, the book seems suitable for younger adults, but overall it seems more fitting for adult readers. However, fantasy fans in general should enjoy this charming tale.