In a small town in the late 1980s, Chen Tiehua, the blacksmith's daughter, guards alone the blacksmith shop left by her father. Zhou Tiesheng, a technician from the county industry bureau, barges in with a demolition notice, but is stunned by the 'spark pattern' flowing on the iron knife in her hand. Their fathers were once sworn brothers, forced apart because of an iron cooperative injustice case, and the spark pattern requires one person to forge and one to watch the fire—together they live, apart they die. Facing foreign buyers and the dark hand of the old case, Chen Tiehua and Zhou Tiesheng go from pointing swords at each other to standing shoulder to shoulder before the furnace, chasing the truth in the furnace fire. In the end, they resolve old grudges with sincerity, make the lost craft reignite sparks, and guard the artisan's backbone and warmth.