Kim Taggart and Antonio Mastrantonio star in this horror movie about a serial killer who terrorizes the unsuspecting citizens of a small American town. Two detectives attempt to crack the complex case after a group of high school kids encounter the deranged murderer--with grisly results. As the case unravels fingers start to point at a high school loner who is seen acting suspiciously, but KNOCK, KNOCK has a few surprises in store as the bloodshed escalates and the film builds towards a dramatic finale.