Retired teacher Luo Wenqing, hiding it from his family, insists on returning to the Qingshigou Primary School to teach, a place he has been away from for over forty years. He used to be a child in the mountains, lifted out of the mountains by his mentor Gu Mingyuan with his life. Now, carrying half a yellowed roster, he steps back onto the podium in a dilapidated classroom. Facing doubts and illness, he not only lights up the hope of left-behind children like Shitou and Xiaoman, but also uncovers a secret about sacrifice and inheritance. This is not the burning of one person, but the passing of lamp after lamp. A belated class will eventually cross the mountains and illuminate a farther path.