Lin Ye, a boiler room worker, is devastated when his uncle, Lin Dashan, dies unexpectedly. Amid his grief, he discovers that his uncle's consciousness has somehow become attached to a black cat. The cat possesses the technical expertise of a Grade Eight master craftsman and guides Lin Ye step by step through equipment failures in dangerous working conditions, including underground ash corridors and high-temperature pipe shafts, while helping him hone his welding skills. Facing hostility from colleagues and repeated life-or-death trials, Lin Ye draws on his uncle's legacy and his own hard work to rise from an ordinary furnace operator to a highly skilled welding expert. He ultimately takes part in major national projects, illuminating the glory of workers with the sparks of his welding torch.