When Laina Michaels receives a message from her friend Blake Redding, her life is turned upside down. She believed that he had died with the rest of the victims of the latest Thinning. He informs her about an underground network taking the children that have been taken to the Thinning and holding them in a underground chamber underneath Vista Point High School, along with the victims from the elementary school. The underground network, or as the victims call it "The Chamber" was formerly ruled by Mason King and then taken over by the guards who worked with him. The government knows nothing about "The Chamber", and neither do the victim's families. They still believe that their children are dead. Laina has to rescue all of the victims, expose "The Chamber", Get back the guy that she fell for, and end The Thinning once and for all, all while not getting caught. One result leads to world peace, and less death, and the other result leads to certain death for Laina and Blake. Which ending will play out in their favor?