Alone in her attic bedroom, teenage Casey (Anna Cobb in a stunning feature debut) becomes immersed in an online role-playing horror game, the World's Fair Challenge. After an initiation, she documents the changes that may or may not be happening to her, adding her experiences to the shuffle of online clips available for the world to see. As she begins to lose herself between dream and reality, a mysterious figure reaches out, claiming to see something special in her uploads.

The film is presented as a compilation of the clips that Casey posts online. It's found footage done right, a compelling and unsettling film that wowed audiences at Sundance. Jane Schoenbrun, the director, said that this movie was a seed from their teenage years staying up late writing scary stories about serial killers and vampires on an online horror message board. "I was a morbid, creative kid still decades away from accepting my trans identity. And for me, the anonymity of this forum was a refuge. Even though the tone of my stories were pretty dark, writing and posting them was a balm."