The Mysterious Mansion (also known as The Mélamare Mystery) is the eighteenth novel in the Arsene Lupin series of books by Maurice Leblanc. The book tells the story of a diamond theft and the kidnapping of Régine Aubry, an actress. Arsene Lupin, under the pseudonym Jean d'Enneris, is hired by jewel magnate Van Houben in an attempt to solve the crime. The mystery deepens however when a second kidnapping takes place, and a history of rivalry and hatred between two families is uncovered.