In the parallel space, the human world and the demon world communicate with each other. People from both worlds among humans can go to the demon world, and monsters can also come to the human world after obtaining the necessary procedures. Their actions are supervised by the Human and Monster Peace Affairs Bureau.
One day, Dr. Yan, a member of the two worlds, was invited by Ling, a noble son of the water tribe in the demon world, to the demon world to attend the centenary ceremony of the annual meeting organized by the Management Bureau. Before leaving, Ling was attacked and seriously injured. In order to help Ling, Yan asked his colleague Dr. Chu Wen to go with him. At the same time, Qin Yu, the eldest lady of the Yu tribe, stole a bronze mirror said to be a sacred artifact of the Yu tribe from the Museum of Humanity. In order to "smuggle" it to the demon world, she asked Yan to help bring the bronze artifact across the border and solve the mystery of the mutation that has troubled the Yu tribe for thousands of years. In order to uncover the hidden evil forces and maintain the peaceful coexistence of the two worlds, Yan embarked on an arduous journey to the demon world to find the truth.
Motto: An unthinking life is not worth living.