故事讲述的是一个极度危险的精神病人从医院逃出，与常人无异般地在街上随意出入。在杀死一名女子后警方在医生的配合下终于找到了线索，与嫌犯展开了一场貌不惊人却暗藏乾坤的搏斗。

1973年以达里奥·阿金图为首拍摄了四部恐怖题材的电视短片《天黑请开门》，且每集均以一段达里奥的口述访谈作为开场。这四部作品虽然都是以犯罪，凶杀为主的传统题材，但是在拍摄风格，以及气氛渲染上已经颇具意大利后期的“Giallo”风格，是非常具有时代意义的恐怖题材的电视作品。

Roberto, a drummer in a rock band, keeps receiving weird phone calls and being followed by a mysterious man. One night he manages to catch up with his persecutor and tries to get him to talk but in the ensuing struggle he accidentally stabs him. He runs away, but he understands his troubles have just begun when the following day he receives an envelope with photos of him killing the man. Someone is killing all his friends and trying to frame him for the murders...