An extreme cold wave strikes Lingang City, plunging temperatures across the entire city and causing widespread power outages. Hundreds of citizens are stranded at Haiyu Plaza, which becomes a temporary shelter for the coastal district. Zhou Du, an engineer at the shopping mall, unexpectedly activates the old city's underground emergency relay system. Working together with medical staff, security personnel, and volunteer citizens, he organizes an orderly self-rescue effort and coordinates with the main rescue teams to reconnect the underground relay network floor by floor, transforming the mall into an emergency refuge ark for the coast. Throughout the long, endless night, ordinary people join their faint lights together to form a lifeline against the bitter cold.