What Happened in Room 4?

Four completely different kids come to a boarding school, not expecting much out of it. But when one of the students goes missing and a threatening note is found on his dorm, his roommate is suspected, the entire school is put on lockdown and no one can leave. The note vividly describes what will happen to the student and the rest of the school if anyone tries to leave or if the police get involved. Since they can't get professional help, the students are forced to look for the kidnapper and prove their friends innocence because if they don't, someone else is going to be next, and you never know who...