In Xinhai City, a bustling city built of steel and concrete, a stray calico cat named "Hui Hui" has long been accustomed to a life of foraging next to trash cans and napping on the outside of the air conditioner. It has seen drunken people smash wine bottles late at night, and heard the roar of sanitation trucks at five in the morning, but it never thought that a curiosity about "human food" would completely change its fate - on a rainy night, Huihui mistakenly ate half a piece of fried chicken with a strange blue light in an abandoned takeout box. When he woke up the next day, he found that not only could he understand human conversations, but his claws could easily tear open the anti-theft net, and he could even reflect the data stream of the surveillance camera in his pupils.
As his body mutates, Hui Hui is forced to be involved in a secret hidden in the shadows of the city: pollutants that humans regard as "industrial waste" are quietly transforming the genes of urban animals; and a group of mysterious people wearing white gloves are searching for "abnormal individuals" in dark alleys with capture nets. In order to survive, Hui Hui must unite with animals that have also mutated - the stray dog "Tiezhi" who can chew through cables, the rat "Zhizhi" who can sense earthquakes in the sewer, and the pigeon "Messenger" who can remember all traffic light patterns - to build their own "underground kingdom" under the eyes of humans, and at the same time uncover the shocking conspiracy behind the "takeaway pollution" related to urban ecology and human greed.
