This book is outside of Marie Lu's typical wheelhouse, but it is sure to please fans of music and magical realism. Nannerl is the older sister of Wolfgang (Wolferl) Mozart in this fantastical tale of historical fiction. This is a tale of music, talent, sibling rivalry, and love. While history remembers Wolferl's story, this book explores what would happen if his older sister's talent had been more appreciated. This book has Wolferl learning from her and them composing together and about them exploring together to the mysterious Kingdom of Back, where nothing is quite as it seems. In addition to covering the story of the talented siblings, this book explores themes of sexism and the power of the patriarchy.