Astronomer and composer William Herschel rescues his sister Caroline from a life of drudgery in Germany and brings her to England and a world of music-making and stargazing. Lina, as Caroline is known, serves as William's assistant and the captain of his exhilaratingly busy household. William is generous, wise, and charismatic, an obsessive genius whom Lina adores and serves with the fervency of a beloved wife. When William suddenly announces that he will be married, Lina watches as her world collapses.