Lilith

Mr. Vane, the protagonist of Lilith, owns a library that seems to be haunted by the former librarian, who looks much like a raven from the brief glimpses he catches of the wraith. After finally encountering the supposed ghost, the mysterious Mr. Raven, Vane learns that Raven had known his father; indeed, Vane's father had visited the strange parallel universe from which Raven comes and goes and now resides therein. Vane follows Raven into the world through a mirror (this symbolistic realm is described as "the region of the seven dimensions", a term taken from Jacob Boehme).