Elizabeth Benton, a sociology graduate student, uses a social media platform called The Den for her thesis project, aiming to measure how many meaningful conversations she can have with strangers online. With help from her friend Sally on the graduate board, she secures a reluctant grant and spends months chatting on the platform, despite concerns from her boyfriend Damien and friends Jenni and Max. Most chats end quickly, but she gathers ample data and remains optimistic.
Elizabeth's account is soon hacked. Her webcam activates without her consent, and a hostile stranger repeatedly tries to contact her. One night, her webcam secretly records her and Damien having sex, and the video is leaked to her graduate board. Later, she witnesses a masked man murdering a young woman live on The Den. The police suspect a hoax, and Max's attempts to trace the hacker fail due to extensive proxy routing.
Damien is abducted during a video chat, and Jenni is later lured to Elizabeth's house by someone posing as her. Jenni is found with fatal wrist wounds in an apparent staged suicide, while the leaked sex video causes Elizabeth's grant to be suspended. The hacker then targets Elizabeth's pregnant sister Lynn, sending disturbing footage of intruders entering her home. Though police surround the property, an attacker posing as an officer retrieves the camera, revealing inside knowledge or infiltration of law enforcement.
Elizabeth's friends are picked off one by one. She watches Max murdered on-screen, while Damien's fate remains uncertain. Returning home, she finds her police protection compromised and kills a masked intruder hiding in her closet, only to be captured outside by another assailant.
Elizabeth wakes chained inside an abandoned building, a camera stapled to her forehead. She is forced to chat with Damien, who warns that their captors are part of a larger network. She watches a video of Max being suffocated and sees Damien dragged away to his presumed death. When one attacker enters her cell to kill her, Elizabeth strangles him with her chain, escapes her restraints, and flees through the dark complex armed only with a hammer.
As she fights her way out, Elizabeth interrogates a young captor, who admits Damien is not there. She surfaces, hijacks a getaway car, but crashes after being rammed by another vehicle. The killers drag her back underground.
The narrative shifts to Brianne, another Den user who earlier chatted with Elizabeth. Brianne receives a video showing Elizabeth being hanged and shot, revealed to be part of a black-market website selling snuff films staged as "narratives" of victims hunted through The Den. A man browsing the site prepares to purchase Brianne's "narrative" before being interrupted by his young son.
