Qingshi Village is battered by days of torrential rain, and the reservoir is nearing a critical level and about to release its floodwaters. While gathering mushrooms, Lin Xiaoyu and Zhao Xinger witness a school of bizarre, sharp-toothed fish attacking a live cow, turning the water red with blood. Yet the entire village dismisses their warning as a joke. Chen Haoran, a university student, recognizes the creatures as piranhas that should never have been there. Thousands of these exotic fish escaped into the reservoir after a fish farm owner illegally raised them and the heavy rains swept them away. Opening the floodgates will send the monstrous fish rushing downstream with the flood; keeping them closed risks a catastrophic dam failure. Racing against time, the villagers discover an abandoned old spillway and risk their lives to open it, diverting the fish into a quarry pit. The dam is saved, but a dark shadow still glides silently beneath the water.