Jiang Yue was the founding chief designer of heavy-duty engines at Hongxing Heavy Machinery Factory. Before the acceptance inspection, he discovered that the No. 3 fuel supply valve had been deliberately tampered with. Instead, Cao Yuanshan, Lin Hui, and others framed him, accusing him of leaking secrets and causing an accident. He died in an abandoned mine, leaving behind fragments of blueprints and his final words: "Don't build machines on your knees." Forty years later, fitter Jiang Hai is fired for exposing a hidden danger in imported equipment. On a rainy night, he enters the mine and inherits Jiang Yue's technical memories and evidence. Joining forces with Shen Qinghe, Zhao Tiesheng, and other veteran workers, he establishes the Jiang Yue Workshop, exposes foreign traders' scheme of reselling refurbished old technology, and investigates the whereabouts of five missing core blueprints. As physical evidence gradually emerges, the conspirators begin to reveal their weaknesses.