Modern archaeological researcher Shen Zhibai falls into a Ming dynasty underground palace, opening his eyes to become Gu Mingchuan, the Ministry of Works supervisor in the fifteenth year of Chongzhen—a cowardly supervisor whose vulnerabilities are held by his superiors and who is sent to just go through the motions. What he takes over is a bird gun explosion case with half a camp of soldiers dead or injured, and the higher-ups are in a hurry to behead the military commander to shut people up. But Shen Zhibai has read The Exploits of Works of Nature to tatters; while others rely on their mouths, he relies on books to tap steel and listen to sound, quench and inspect quality, examine fractures to distinguish sand, and probe the bore to check slag. Four tests in court hammer out the raw and secondary materials to their original forms. The more he investigates, the clearer he understands that the hand behind the scenes is all the more eager to silence him by burning inspection slips, framing him with silver, and dispatching assassins at night. With a four-day deadline and the whole city as witness—a single broken matchlock drags out a dark chain from the material inspection office all the way to the imperial court.