A serial killer known as Cinderhella is on the loose and preying on Grizzly Lake High's student body. The principal is certain Cinderhella is a disgruntled student at the school and puts the likely suspects - including suicidal Riley, self-absorbed Ione, and hipster Clapton - in all-day (10:00 AM–10:00 PM) detention on prom night. Potentially trapped in a room with a murderer, Riley, Ione, and Clapton are forced to work together to stop Cinderhella from killing again, unaware that they're dealing with sinister supernatural forces.