The Shadow Box is an evil Mystery House and is responsible for countless deaths across the globe.
Like its fellow Mystery Houses, it is a powerful, living magical artifact. Unlike the House of Refuge, who is friendly and helpful, the Shadow Box is dangerous and highly aggressive. According to Jenkins, it has left a string of victims of all ages and demographics across the globe in what can best be described as "feeding cycles".
It is also very cautious as, despite being known of by the Librarians, none have managed to have a direct encounter with it.
It is possible that the Shadow Box is the same house as the House of Refuge, as the Shadow Box has been known to move around and has been active for the past hundred years (with the first confirmed sighting in 1883), while the Bloody Benders found the House of Refuge in the 1800s.