In 1972, Stephens Sanitarium was the scene of a brutal mass murder. Forty years later, Sam Withers, the only known survivor, arrives at Green Park mental institution. Dr. William Matthews, a successful New York doctor fighting his own inner demons, accepts a position at the small-town clinic and is assigned Sam’s problematic case.

Sam’s arrival at Green Park triggers strange behaviors in the staff members and residents. Even the building itself takes on a menacing nuance. Driven to stop the madness, Dr. Matthews leads the Green Park staff in a plan to save themselves and the remaining patients; however, it’s not until he ventures into the basement that he comes face-to-face with the perverse truth.