In a highly-structured eighteenth-century society, the city state of Angelio is known for two things: its music, and its guardian, the Archangel Michael.

At Angelio's music school—nicknamed the Cage of Nightingales—castrato singer Carlo is headed for fame at the opera ... at the price of personal freedom. Charity pupil Tammo hates the school and everyone in it, and wants to live in the woods, charming birds with his flute.

When Tammo meets Carlo, their lives change forever. With the help of the Archangel, they can grant to each other whatever their hearts desire. But staying true isn't easy, and their choices will affect not just their futures, but that of Celestina—a young aristocrat destined to be the third person in their relationship.