*CUT TO THE CHASE*
NOTE: This spoiler was submitted by Jeremy
The movie starts in a college psychology classroom. As the students are gathering in their seats, the professor announces to them that one of their classmates, Marina Mills (Liesl Ahlers), has committed suicide over the weekend. All the students are stunned, but most disturbed is a girl named Laura Woodson (Alycia Debnam-Carey).
Two weeks earlier, Laura was a normal popular college girl, living with her best friends Olivia (Brit Morgan), Izzy (Brooke Markham), and Gustavo (Sean Marquette). Her boyfriend is Tyler (William Moseley). Laura is also very active on social media, having over 800 friends on Facebook. During lunch, she catches Marina's attention, and she later sends Laura a friend request. Laura sees that Marina has 0 friends on Facebook. However, she finds Marina's drawings and video animations to be intriguing, so she starts to casually hang out with Marina at school.
Soon, Marina grows obsessive toward Laura, even photoshopping herself into one of Laura's selfies. The drawings on her page also get freakier with gruesome and haunting images involving wasps and darkness. Marina sends Laura multiple messages, which start to make her uncomfortable.
On Laura's birthday, Marina tries to invite herself to hang out with Laura, to which Olivia and Izzy object to. Laura tells Marina that she's only going out to dinner with Tyler. She ends up at a surprise dinner with all her friends, who take pictures and tag her in them on Facebook. Marina sees them and she gets upset.
The next day, Marina angrily confronts Laura in the cafeteria. She even claims to have made her a birthday present that she was working on for two weeks (despite only meeting her around that time). Laura tries to calm Marina down, only for the girl to try and physically attack Laura. She shoves Marina in defense and makes her hood fall back, revealing a burnt bald spot on her head. Marina runs away.
That night, Marina desperately tries to apologize to Laura for how she acted. Having had enough, Laura unfriends Marina. After seeing this, Marina hangs herself while setting the place on fire.
After Marina's suicide is reported, Laura sees a video of the incident, in which Marina holds her present to Laura (a drawing of Laura) to the camera before crumpling it and hanging/flaming herself. The video uploads itself to Laura's profile, and she is unable to delete it. This causes others to unfriend her. She is even unable to delete her account. Laura asks her friend Kobe (Connor Paolo) for help in undoing the video. When they try looking into it, they see that the code on the video is not like any normal code for other videos.
Izzy calls Gustavo (they're dating) as she returns to their dorm. Gustavo then has Marina added to his friends list on Facebook. He sees some freaky imagery on his computer before it shuts off and leaves the screen with his still reflection, even when he's not looking at it. Gustavo then walks into the hallway and sees nothing but what appear to be two young boys with horribly disfigured faces. He runs into the elevator, which goes dark. He takes out a lighter and sees a hand reach for him. Izzy arrives and sees the elevator doors open, revealing Gustavo in a possessed state smashing his head against the walls until he drops dead.
Gustavo's friends mourn him, but the elevator footage of his death appears on Laura's Facebook page, leading more people to consider her sick and unfriend her, no matter how much she tries to delete it. Even Izzy, who's been hospitalized due to the shock of seeing her boyfriend die, doesn't want anything to do with Laura. When Laura tries to post a message saying she's not posting the videos, Marina's spirit writes "u will know what it feels like to be lonely :)".
Laura and Kobe track down Marina's birth records and find out the boarding school where she originally grew up. They visit the place, and Laura learns from the headmistress that Marina was brought there as a child after her mother perished in a fire. She gave birth to Marina right before she died. During her time at the school, Marina was picked on by two boys, both of whom were later found dead with their faces mutilated from wasp stings (the same boys Gustavo saw).
Meanwhile, Marina adds Izzy on Facebook. Izzy leaves her room under the illusion that she is alone and wandering around helplessly. She is then trapped in a room by Marina, who possesses Izzy and makes her tear out her hair before slitting her throat.
When Laura and Kobe drive back, they accidentally hit Olivia with their car, as she has come under Marina's possession as well and was led to the car's path. In the hospital, Olivia is possessed again when she attacks a detective and takes his gun, which she uses to blow her brains out.
Laura and Kobe determine that Marina performed a ritual by staring into a black mirror (her laptop screen) and has been using her spirit to get revenge on Laura. They find out where she previously lived and head to the burnt-down house to find the laptop and destroy it. However, Kobe ends up getting possessed by Marina. He stabs Laura when he figures the hauntings will stop if she's dead. She overpowers Kobe and escapes him.
Tyler drives out to the town to find a now manic Kobe trying to find Laura. Unbeknownst to them, she has taken a cab to a factory where she figures Marina killed herself. Laura then gets into a video chat with her mother, who also gets possessed by Marina. She takes a knife to kill herself offscreen while Laura is helpless to do anything.
Tyler finds Laura, but he is quickly stabbed through the throat by Kobe. He chases after Laura but then gets stung to death by Marina's swarm of wasps. Growing tired, Laura sees an apparition of a young Marina, saying she only wanted to be her best friend. When Laura finds Marina's body and laptop, she is taken into one of her creepy posts, specifically a dark forest. When Laura turns around, Marina's spirit lunges at her.
Some time later, Laura is back in school, but with absolutely no friends. She looks upon another group of girls the way Marina looked at her. She looks on her Facebook profile, which has the picture of her and Marina. Laura looks at the audience with dead eyes, indicating Marina has now taken over her body.