"Unlocked" is book 8.5 in the popular upper-middle-grade fantasy series, Keeper of the Lost Cities, by Shannon Messenger. This volume serves as both a comprehensive guide to the intricate world and characters, and a significant novella that continues Sophie Foster's journey. Sophie, a twelve-year-old elf with extraordinary abilities, was raised by humans before being brought to the hidden Lost Cities, where she attends an elvin academy and becomes embroiled in a conflict between a rebel organization, the Black Swan, and criminal extremists, the Neverseen. The series explores themes of identity, belonging, friendship, and the search for family, as Sophie uncovers secrets about her origins and faces moral dilemmas. Parents should be aware of themes of peril, conflict, and some character trauma, particularly regarding family issues and the ongoing battle between factions.