Boo (2005)

On a chilling Halloween night, Emmett, Freddy, Marie, Kevin and his skeptical girlfriend Jessie venture into the decaying corridors of an abandoned hospital. Unbeknownst to them, young Allan seeks out Arlo Ray Baines, an old acquaintance of his father. Allan desperately hopes Arlo can help him find his sister, Meg, who vanished within those very walls. Fate intertwines these two groups as they converge on the asylum's haunted third floor. Within the mental institution's grim heart, their separate searches will collide, revealing the hospital's sinister secrets. The night promises terror and unexpected alliances.