On the streets of Los Angeles, a disaffected Tommy Walcott is invited by actor Andy Samberg to join him in an unmarked stretch limo. In the limo, Andy reveals that the company that hired him to approach Tommy has been tracking Tommy for a while, and asks Tommy if he would like to “continue on this adventure,” to which Tommy promptly agrees. Tommy is taken to a warehouse, where two hosts invite him to take part in a reality game show hosted on the dark web. The rules of the game stipulate that Tommy must survive 30 days while being hunted by hunters attempting to kill him. Should he survive, he will receive one million dollars. Tommy is hesitant at first to put other people’s lives at risk by being in proximity to them, but the hosts reassure him that he will only be killed when he is alone. Upon hearing this, Tommy agrees to participate in the game believing that he has identified a loophole wherein he can win by keeping a friend or family member near him at all times.
Hearing his pitch, Tommy’s mother Laurie, with whom he is living, and two older sisters Amy and Mary are reluctant to believe him and refuse to participate in the game. They believe Tommy is deluding himself with a game to distract himself from his breakup with his long-term girlfriend, Theresa, two years prior. Tommy makes a Craigslist post looking for strangers who will agree to hang out with him. Days pass without any sighting of hunters. On the night of day 5, Tommy is startled awake by an abrupt noise and goes to investigate, finding what he believes to be a miniature camera in front of the door, which has been left ajar. Believing this to be the work of the show’s silent production assistant ninjas, he calls his mother, who is working the night shift at the hospital as a nurse. After being dismissed by his mother, Tommy crashes at Amy’s apartment with her boyfriend, Malcolm. That night, Tommy awakens to find Malcolm missing and spots a threatening figure standing outside the apartment. A frightened Tommy breaks through Malcolm’s bathroom door so that he can join Malcolm and avoid being killed by the hunter seemingly wielding a rifle outside the window. Startled, Malcolm evicts Tommy in the middle of the night, giving Tommy no choice but to hire a homeless stranger, James, to be his shadow.
The next morning, Amy confronts Tommy for frightening Malcolm and inviting a stranger into their mother’s home. Tommy spends the next week safely roaming the city with James as his shadow. On the night of day 13, Tommy joins Mary outside a night club after James stops answering his calls. Stepping away briefly to make a call to a stranger responding to his Craigslist post, Tommy is attacked by a tall man dressed as Michael Jackson, only narrowly escaping. The next day, Tommy and James meet Maddy, the Craigslist responder who claims to be another participant in the game with 15 days remaining. Tommy proposes that they spend the day together to avoid being killed. Maddy quickly warms up to Tommy after challenging him to confront his ex-girlfriend about their breakup and spending the night with him at a dance club. That night, Tommy is awakened in Maddy’s bed by a troupe of production assistant ninjas warning him that he is not as safe as he thinks. Tommy convinces Maddy to move in with him at a local motel. There, they are threatened by a hunter dressed as Mario claiming to be the manager and plumber for the motel. Tommy and Maddy spend the next few days growing closer to each other in isolation. On day 19, Tommy receives another response to his Craigslist post claiming to have important information about the game, however Maddy is reluctant to let Tommy respond. Tommy brings Maddy to meet Charlie, who explains that the game show is billed as a comedy called DOG (“Delusions of Grandeur”) and that they are the punchline. Maddy is suddenly unsettled and decides to return home without Tommy.
A frustrated Tommy returns to live with Amy and Malcolm in their apartment, where he loudly rebukes the show’s viewers and threatens to murder Andy Samberg if the hunters hurt Maddy. That night, Tommy is again awakened by the production assistants and led to another limo, where Tommy is surprised to see his estranged father of thirty years. He informs Tommy that Wayne Brady, hired by the show runners, asked him to tell Tommy that Maddy is unhurt and encourages Tommy to go win her back after expressing regret about how he abandoned his own family. The next morning, Tommy and James go to Maddy’s home, but Maddy reveals that she was lying about being a part of the game out of boredom, believing it to be a role play dating scenario. Tommy receives a cryptic text from his mother asking him to come home due to an emergency. Running home on foot, he is attacked by a woman impersonating Ellen DeGeneres, losing a tooth but escaping once again when James appears by his side. He arrives home to an intervention staged by his family, telling him that it’s time to end his delusions. Tommy runs away and spends the night with James at a homeless encampment, where Tommy promises to use some of his prize money to buy James a place. James reveals to Tommy that his name is in fact Walter, and that Tommy had just assumed his name was James when they met. On the morning of day 27, Tommy wakes up alone but is able to escape and spend the next few nights at another encampment under a bridge, growing increasingly unkempt. On his final night, Tommy is awakened by the production assistants, who explain that they were the ones who relocated Walter to a local motel so that Tommy could have a more exciting ending. Tommy is asked to leave the encampment and await a limo to pick him up. While waiting, he escapes a hunter dressed as a cowboy who explains that the whole game is set up just for him, drawing characters from his interests and past experiences with his father and ex-girlfriend. In the limo, he reunites with Andy Samberg, who offers him the choice to forgo his cash prize to return home safely, but Tommy refuses.
Tommy arrives back at the warehouse he was initially taken to, where he is chased by a sumo wrestler, a man dressed as comedian Sinbad, and a Samurai. He arrives back at the room where he first agreed to join the game, but finds it abandoned. Suddenly, the stage lights turn on and the hosts enter the room, followed by a crowd of production assistants and hunters, who all congratulate him for being the first winner of the game. Tommy returns home vindicated, but reveals to his family a final twist that his prize money is being delivered as 250 monthly (i.e. 21 years) installments of 4,000 Greenlandic krone (i.e. US$636). Tommy invites Walter to be his roommate at his new apartment. Before returning home, Tommy decides to reconnect with Maddy and the screen cuts to black as he nervously knocks on her door.