London Overhead, a fantastical city above London, is invisible except to its winged human Librae. Eleven-year-old Astrid, new to this world, loves London Overhead and was eager to finally fledge—and fly. Disastrously, though, her wings don’t work, which may spell banishment, a fate her unfledged Pakistani British friend, Pent, also faces. A monthlong festival brings the mysterious organizers, the Birthday Folk, to town. The festivities include a perilous competition with a prize “based on the winner’s deepest longings.” Determined to fix her wings in time, Astrid enters; she arrived in London Overhead weak and with paper-white skin from having grown up in a rhubarb shed, and she’s excited about the strength she’s since gained. But others are equally desperate to win—and someone is determined to ensure that Astrid doesn’t survive. Sympathetic Astrid copes with trials including jealousy, despair, friendship conflicts, scornful teachers, and fear for her life. She also yearns to change the city government’s blatant unfairness and classism. While the layered characters confront believable struggles, keeping track of the large cast can be difficult. Though this exceptionally creative world is lush with sensory descriptions, even with Kurtz’ opening illustration as guide, understanding the city’s structure and functioning might challenge readers. A plethora of details slows the first chapters.