Lu Chang'an does not know martial arts and takes over the debt-ridden Longfeng Escort Agency of three thousand taels. Others rely on sabers and spears in escorting, but he relies solely on an abacus, a piece of contract, selfless dedication, and integrity to conduct business across the realm. Undercurrents surge in the northern border grain routes, surrounded by corruption and bandit threats. He calculates meticulously, weighs pros and cons, uses account books as a weapon to protect grain and the people, and props up the Longfeng lineage amidst troubled times.