22 thousand fans are in Las Vegas for a life-affirming celebration of country music. Headliner Jason Aldean launches into his first set. Then the gunfire starts. They are trapped in a killing field. Amid the confusion and chaos, friends and families try to flee but get separated. An off duty firefighter rescues the wounded as instinct takes over. A Black man who felt unwelcome at first risks his life to help. Running left or running right could mean life or death.