An outbreak of disease suddenly strikes the borders of Yunzhou, where a cold-like illness spreads rapidly. Sun Zhenyue, the general guarding the region, leads his subordinates to kneel before Xu Simiao, a renowned former imperial physician, begging him to save the soldiers and civilians of Yunzhou. Xu Simiao has already sensed that the outbreak is far from ordinary, but for the safety of everyone in Yunzhou, he steps forward despite the danger to his own life. After establishing three strict conditions with Sun Zhenyue, he heads to the military camp to treat the sick. There, Xu Simiao quickly discovers that this is no ordinary cold, but a devastating epidemic unseen in a century! He pays for the medicine out of his own pocket and treats the soldiers, gradually bringing the epidemic under control. However, Cai Huaide, a renowned physician sent by the imperial court, insists that the illness is merely a common cold and accuses Xu Simiao of being a spy who prescribes medicine recklessly!