Gu Shi'an, an emergency medicine resident at Jiangcheng First Hospital, is often criticized for his seemingly careless attitude. Yet in critical moments, he can identify hidden medical conditions and save countless critically ill patients. He once worked overseas in a joint cardiac medical program, but three years ago, an equipment accident that was covered up led him to conceal his past and return to China to hone his skills in emergency medicine. Amid one life-and-death test after another, Gu Shi'an and his emergency department colleagues work together to save lives and piece together the long-buried truth. Rejecting the idea of individual heroism, he strives to turn clinical experience into standardized treatment protocols, protecting lives with the true heart of a physician.