Ethan is a tech-savvy high school student living across the street from Harold, a grumpy old man who prefers solitude and is known for his rude demeanor. Harold’s antisocial behavior includes ignoring visitors and threatening to dismember a neighbor's dog. In an attempt to lighten their school project, Ethan and his friend Sean decide to convince Harold that his house is haunted. Knowing Harold's routine of going out shopping and never locking his doors, they purchase an array of electronic gadgets using Sean's dad's credit card, and carefully plan their prank at Harold's home while he is out.
As they set up hidden cameras throughout the house, they become intrigued by the locked cellar door, which stands in stark contrast to his otherwise unlocked home. Through remote manipulation, the boys begin their experiment observing Harold's responses from Ethan's bedroom as they control the lights and music player, leading to peculiar moments where Harold doesn't show fear. Instead, the audience witnesses flashbacks of his late wife imploring him to repair the screen door or inviting him to dance—a stark reminder of the love he lost. When the flickering lights trigger a security alarm, Officer Palmer visits, but Harold brusquely dismisses him.
The boys grow increasingly curious as they notice Harold frequently retreating to his cellar during these supernatural occurrences, to the point where he no longer leaves his house. Convinced that he is hiding something sinister, they anonymously alert the police about screams from the house. Officer Palmer arrives once again, but Harold easily allays his suspicions, leaving Ethan frustrated as he believes something crucial was overlooked.
Their mission is propelled by a deeper motive; Ethan harbors resentment against Harold for a past incident involving his father, who was jailed after an altercation with Ethan's mother. Tensions rise between Ethan and Sean when a party at Ethan's house leads to the discovery of a hidden camera, causing Sean to rage against Ethan’s invasive actions. Distrust creates a rift in their friendship, but Ethan remains determined to investigate further.
When an unexpected incident with Harold's cat knocks over a hidden camera, Ethan, while sneaking back into the house to recover it, stumbles upon the unlocked cellar. Curiosity overwhelms him and he descends into the cellar, uncovering a shrine dedicated to Harold's deceased wife. In a nervous moment, he rings a hand bell he picks up, inadvertently waking Harold. In a bid to avoid detection, Ethan dashes back upstairs and locks the cellar door, but the moment escalates quickly. Harold, believing the bell signals his wife, emerges with a handgun and tragically takes his own life.
In the wake of this shocking event, Sean and Ethan scramble to erase any evidence of their surveillance before the police arrive. However, Officer Palmer, who was in the area, hears the gunshot and arrives to apprehend the boys instantly. A series of flashbacks reveal the true source of Harold's despair: his profound grief over his wife’s death and his belief that she had been communicating with him through the paranormal happenings.
Ultimately, the boys face a trial for their actions, which culminates in probation and community service. After the court session, as their paths diverge—Sean heads off to his family while Ethan is left amidst a throng of reporters—a small yet poignant smile forms on his face, suggesting a complex blend of emotions following the ordeal they have endured.
