In the future, due to the great catastrophe suffered by mankind, a few people moved from the ground to underground life. The original design of this huge underground city can only maintain operation for 200 years, and the city has only lights as the only lighting tool. However, as time goes by, 200 years will soon come, and the design life of the city core is about to end. The number of power outages in the city is increasing, and the light on which they depend for survival is about to disappear in this glimmering city. As good friends, Lina (Saoirse Ronan) and Duan (Harry Treadaway) often play in the complex pipes in the glimmering city. One day, Lina found an ancient document that recorded how to get out of the glimmering city. Seeing that the lights of the glimmering city are about to go out, what secrets are there outside this city? Is it a bright light? Lina and Duan decided to follow the guidance of this ancient document, walk out of the city, and go to see the outside world to save the city that is about to go out.