高考前夕，高三男生林昊在凌晨四点坠落于班主任家阳台上当场死亡，班主任卢雯回家发现后报警，接受警察调查,为了保护曾与林昊有爱慕关系的女儿卢筱珊该影响学业，向警察做了伪证，为女儿和自己都提供不在场证明。卢雯等警方排除他杀，将尸体运走后，对刚考完模考的女儿进行质问。长期在极端教育下的女儿卢筱珊心理扭曲，面对步步紧逼把自己关进了“牢房”卫生间，回忆起和林昊、母亲卢雯发生的种种事件，一直到林昊死亡的前夜……

On the eve of college entrance examination, Lin Hao fell towards the balcony of head teacher's home, and died on the spot. Lu Wen, head teacher, called the police immediately when she saw this. In order to protect her daughter, who had been in relationship with Lin Hao, Lu Wen lied and perjured her and her daughter, offering an alibi to the police. When the police ruled out murder, Lu Wen questioned her daughter who had just finished the model test. Exposed in the extreme education for a long time, Lu Xiaoshan was psychologically distorted. Under the pressure of her mother, Lu Xiaoshan locked herself in the bathroom, recalling those affairs with Lin Hao and Lu Wen, which happened before the death of Lin Hao.