10:00 a.m. The principal of Opportunity, Alabama's high school finishes her speech, welcoming the entire student body to a new semester and encouraging them to excel and achieve. 10:02 a.m. The students get up to leave the auditorium for their next class. 10:03 The auditorium doors won't open. 10:05 Someone starts shooting. Told over the span of 54 harrowing minutes from four different perspectives, terror reigns as one student's calculated revenge turns into the ultimate game of survival.