In late-eighteenth-century Ireland, Caroline Ainsworth learns that her life is not what it seems when her father, Arthur, an astronomer gone blind from staring at the sun, throws himself from his rooftop observatory. His vain search for an unknown planet and jealousy over astronomer William Herschel's discovery of Uranus had driven him to madness. Grief-stricken, Caroline leaves Ireland for London. But her father has left behind a cryptic atlas that holds the secret to finding a new world at the edge of the sky. As Caroline reluctantly resumes her father's work, she must confront her own longings, including her love for her father's former assistant, the tinkering blacksmith Finnegan O'Siodha. Then Ireland is swept into rebellion, and Catherine and Finnegan are plunged into its violence. A novel about the obsessions of the age—scientific inquiry, geographic discovery, political reformation, but above all, astronomy— encapsulates the quest for knowledge and for human connection. It is rich, far-reaching, and unforgettable.