In Homewood, Alabama, we meet Simon McNally, a man grappling with paranoid schizophrenia, who is haunted by intense hallucinations and the harsh voice of his late father, which constantly berates him. Recently discharged from a mental institution after nearly ten years, Simon finds it difficult to engage in everyday activities, forcing his older sister, DeeDee McNally, to shoulder the financial responsibilities of their lives.
One day, Simon witnesses a disturbing incident where a young woman is abducted by a man whose face he cannot clearly perceive. His father’s voice taunts him, convincing Simon that it is just a figment of his imagination and that he lacks the bravery to intervene. Despite this, Simon becomes determined to help the woman. He reports the incident to local detective Glover, who, relying on her previous knowledge of Simon’s violent outbursts connected to his illness, dismisses his claims after investigating the van's license plate, which turns out to belong to a car registered hundreds of miles away.
In his quest for help, Simon turns to his neighbor Ed Deerman, a recently retired campus security guard. Though initially hesitant due to Simon's history, Ed ultimately decides to assist him. They brainstorm and decide to look up license plates that resemble the one Simon saw. At the department of motor vehicles, Ed tries to persuade the staff to provide information about plate owners. However, Simon becomes overwhelmed by the situation and has a violent outburst when met with resistance. As they retreat to Ed's car, a repetitive sound from Ed's pen surprisingly calms Simon. They head to a local area to question some sex workers based on Simon’s description of the woman, but their efforts lead to a confrontation, ending in Ed's car being vandalized. Frustrated, Ed admits he never believed Simon's account, causing Simon to choose to continue his investigation alone. However, Ed's conscience drives him to follow and support Simon once more.
To gather more information, Ed resorts to blackmailing his replacement at campus security, leveraging his connections to investigate vehicle ownership details. Their search leads them to multiple vehicle owners, eventually connecting them to Kurt's Auto Salvage. Upon inspecting the premises, they find the van with its plates removed, indicating it was being operated with stolen tags and providing no direct leads. Just then, Simon hears a scream and impulsively dashes toward a car, convinced the woman is inside. Ed tries to restrain him, claiming there was no scream and that the girl does not exist.
That night, tensions rise as Simon and DeeDee clash over his feelings of abandonment when she chose to leave him with their father. Meanwhile, Ed becomes a target of the kidnapper in his home. Witnessing the attack, Simon rushes to help Ed. In a chaotic struggle, they inadvertently kill the abductor and seize his phone, which reveals only two contacts—one being Kurt. They head to DeeDee's workplace for assistance with Ed's injuries while evading the police, who are now searching for them due to the shooting.
The next day, Simon and Ed confront Kurt, and upon observing a clock on the wall, Simon discovers it conceals a safe, much like Ed’s at home. Inside, they uncover women’s passports, including one for Anya, the abducted woman. Kurt then reveals that the abductor is a sex trafficker and that Anya had been punished for attempting to escape. Armed with this information, they contact the police while leaving the passports behind as evidence for Glover.
Upon arriving at the abductor's residence, Simon faces another episode of his father's taunting, leading him to momentarily break down. Ed reassures him, calming Simon by using the clicking pen, which he gifts to him for future comfort. They proceed to search the home, finding it deserted until they are confronted by the abductor's mother, who soon tries to flee. This prompts them to investigate further where they locate a secret door, revealing Anya hidden inside.
As the police finally arrive, they safely escort Anya away and apprehend Simon and Ed. In a quiet moment, Glover acknowledges their bravery with a subtle congratulatory gesture. Simon and Ed share a significant glance, a breakthrough for Simon as maintaining eye contact had previously been a challenge for him.
