In the human microscopic world, new red blood cell Miaocuiqiao Xiaomao starts the working daily routine of delivering oxygen. On the first day on the job, the blood vessel erupts into a massive oxygen transport traffic jam, and the culprit is the invading pneumococcus. At the critical moment, white blood cell Daodun makes an appearance, repelling the bacteria and saving the trapped red blood cells. But the cunning pneumococcus quietly hides inside Miaocuiqiao Xiaomao's oxygen transport vehicle, escapes Daodun's inspection, and sneaks deep into the body. Thereafter, Miaocuiqiao Xiaomao continually encounters crises in transport missions one after another, and together with protector Daodun, welcomes consecutive challenges in the busy cellular world.