Casey, a lonely teenage girl living with her single father, decides to record herself taking the viral "World's Fair Challenge". She states "I want to go to the World's Fair" three times on camera, pricks her finger, smears some of her blood on her laptop computer screen, and watches a short
strobe light video, before saying she will post updates if she starts to notice any "changes".
Other World's Fair challengers record and post their own psychological and physical changes. In Casey's next video, she recounts bouts of
sleepwalking she experienced when she was younger and says she has begun feeling similarly since taking the challenge. Late one night, she sneaks into her shed, where she finds her father's
shotgun. She then watches an
ASMR video of a young woman calming someone after a nightmare before a disturbing video made to her from user "JLB" plays, featuring Casey's distorted face along with the messages "YOU ARE IN TROUBLE" and "I NEED TO TALK TO YOU."
Casey reaches out to JLB, a collaborator with other World's Fair challengers, and speaks with him over
Skype. JLB claims to worry about Casey after the symptoms she reported in her last post, and encourages her to keep making videos so he can monitor her wellbeing. JLB is revealed to be an equally lonely middle-aged man who spends his time watching other people's World's Fair videos.