Modern youth Xu Zhou accidentally falls into an ancient city and crashes into an inn facing a business closure crisis. Facing loophole-ridden accounts, he relies on meticulous observation and accounting skills to join hands with the intelligent and decisive A Ning and the steady and reliable Gu Shu to audit the accounts. From duplicate bookkeeping and abnormal imprints to replaced ledger pages, everyone gradually finds clues, discovering that Zhao Ping attempts to seize the inn through fake accounts and transfer documents. Everyone insists on letting the evidence speak, and Constable Zhou verifies it according to the law, so the inn finally postpones its closure. Xu Zhou, who temporarily cannot find a way back home, is invited to stay and serve as the accountant, winning trust with his strength. Unexpectedly, an old ledger book turns its own pages and even records his room rent.