Will Harper, a dedicated psychiatrist, resides in a cozy home with his two grieving daughters, Sadie and Sawyer. Since the tragic loss of their mother in a car accident, the family has been struggling with deep emotional scars. To help heal the children's trauma, Dr. Weller serves as a lady psychiatrist, though Will remains distant from the therapy sessions.
One unexpected day, a disheveled man named Lester Billings arrives at Will's office seeking help. He recounts a chilling story about a closet monster that has haunted his family, allegedly responsible for the mysterious deaths of his three young children: Denny, Shirl, and Andy, whom he claims were actually victims of a sinister entity rather than the misdiagnosed SIDS. Lester presents drawings of the creature and ominously states that Andy was found choked. Worried by Lester’s erratic demeanor, Will quickly calls the police, sensing danger in his own home.
Meanwhile, Sadie comes home early from school, upset after an altercation involving her classmate, Natalie, instigated by Natalie’s thoughtless comments. Shortly after, tragedy strikes: Lester is discovered hanging lifelessly in a closet, propelling Will's family into a new realm of terror as the Boogeyman emerges to torment them.
Sawyer is the first to witness the dark figure creeping around at night. In one particularly eerie incident, Sadie tries to help Sawyer with a loose tooth by tying it to a door, only for the door to ominously swing open on its own, yanking it away. An innocent slumber party turns frightening as Sadie and her friends experiment with marijuana, leading to a gruesome surprise when Sadie vomits up the string that had once tied to Sawyer's tooth.
Curiosity compels Sadie to explore the closet where Lester met his end, but she soon finds herself trapped inside, confronted by the terrifying half-human, half-insect Boogeyman. As tensions rise, Natalie's insensitive remarks lead to further conflict among the girls, resulting in them leaving Sadie isolated in her unease. Determined to uncover the truth, Sadie digs deeper into Lester's life and, accompanied by Bethany, visits Lester’s dilapidated home, where Rita, Lester’s widow, armed and desperate, claims to know the creature's vulnerabilities.
As the haunting intensifies, culminating in Sawyer being hospitalized after a violent encounter, the gravity of the situation becomes apparent—this is no mere figment of their grief. An urgent call from Rita draws Sadie back, where a plan to trap the Boogeyman is conceived, but it comes with perilous consequences.
In a moment of sacrifice, Rita tries to ensnare the creature, but it ultimately leads to her demise, freeing Sadie in her final moments. Meanwhile, Will's perception of their struggles is challenged when he finds Sawyer surrounded by Christmas lights as a defense against the Boogeyman. A reunion with Sadie fosters hope to confront their fears together.
As they journey into the basement where their father is held captive, they reunite and glean strength from memories of their mother. With a flicker of faith, Sadie believes their mother is guiding them, empowering her to wield light against the darkness. Armed with makeshift weapons, including a flamethrower, they make a final stand against the monstrous entity, ultimately immolating it.
The following day, the family seeks closure with Dr. Weller, marking a pivotal turning point in their healing process. As they prepare to leave, Sadie notices the closet in Dr. Weller's office slightly ajar, and a chill runs down her spine. She hesitates before braving the threshold, only to be met with an eerie presence. Dr. Weller emerges, questioning if she can assist, leaving Sadie to slam the closet door shut, a haunting reminder that some fears may never truly fade away.
