A long spy mystery. A secret factory in the vast prairie, sealed and guarded at all levels, as solid as a copper wall. Only the underground plumbing works tightly connect this graded and isolated factory. The "plumbing drawings" became the key to getting to the heart of the factory, and it also changed the fate of plumber Yingzi. The "saboteur" appears. Who is he and who is the mole? A life-and-death battle begins.
