The Invisible Girl by Mary Shelley

A young woman vanishes just before her wedding, and her fiancé, devastated, refuses to believe she is dead. Years later, he discovers a hidden part of the house where she has been secretly living in sorrow and isolation. The plot is a romantic mystery with a bittersweet resolution. A tale of lost love, misunderstanding, and devotion. Sometimes the ghost is only a girl waiting to be found.