From Wikipedia:Peter is an eight-year-old boy living with his overbearing, yet emotionally distant parents Carol and Mark. He is often bullied at school and has no friends or any social life. One day, Peter elects to stay inside during recess, and earns some sympathy from his substitute teacher Miss Devine. Despite having plans to go trick-or-treating on Halloween Night, his parents forbid him due to the disappearance of a young girl several years ago.Later that night, Peter is awoken by a tapping sound coming from inside the bedroom walls. Both his parents strongly deny these occurrences, insisting that he is imagining them. Over the next few days, Peter continues to talk with the mysterious entity, who he learns is named "Sarah". Sarah claims that she was trapped in the walls by Peter's parents, calling them "evil"; leaving Peter disturbed.Devine becomes concerned after seeing a picture that Peter drew of Sarah asking for help in a dark room. Following a meeting with Peter's parents, they wave her off and, later on, Carol confronts and admonishes him for bringing his delusions into public scrutiny. Sarah continues to convince Peter that his parents are bad people.At school, Brian, a bully, destroys Peter's prize pumpkin. Spurred on by Sarah's advice, Peter pushes Brian down the stairs, breaking his leg. After being expelled from school, Peter's parents punish him by locking Peter in the basement, concealed behind a refrigerator. Inside the basement, Peter discovers a pit covered with a grate.Devine visits to check up on Peter, but is chased away and intimidated by Mark, who has a gash on his arm that he claims is from doing remodeling work on the house. Eventually, Peter is let out of the basement and reconnects with Sarah, who claims that she is Peter's older sister, having been locked away by their parents after deciding that they didn't want her anymore. Sarah convinces Peter that his parents are planning to kill her and that they will imprison him in the walls. His only chance, to avoid sharing her fate, is to kill his parents, which he does by slipping rat poison into their soup at dinner. Both parents try to stop him, but they succumb to the poisoning before they manage to do so, with Carol warning him to "not let her out".Peter unlocks another hidden door, located behind the grandfather clock in the parent's bedroom. Sarah crawls out, although it is dark she does not seem human. Sarah reveals to Peter that she has been deceiving and manipulating him into exacting revenge on his parents for locking her away, and that she resents Peter for being able to live a normal life. Brian and his cousins then show up at the house, planning to get revenge on Peter, but they are all killed by Sarah. Devine also shows up, summoned to the house by a phone call from Peter, and the two of them manage to imprison Sarah back in the pit of the basement, but Sarah warns Peter that she will eventually escape, and that she will always haunt him.