A devastating flood in his childhood took Jiang Yuan's parents away, inspiring him to make a solemn vow to build dams. Twenty years later, Jiang Yuan returns to Yunjiang as chief engineer. From the moment he takes office, he faces internal hostility, provocation from a gravel pit owner, and resistance from villagers reluctant to relocate. After reuniting with his childhood sweetheart, Lin Qinghe, the truth about his past finally resolves the villagers' doubts. When torrential rains strike, Jiang Yuan leads the villagers in a desperate fight to protect the embankment, earning their trust through sincerity. He provides free technical training for the villagers and roots out corruption and wrongdoing. Ultimately, he completes the Yunjiang Dam and fulfills his promise to protect the lights in thousands of homes.