It is rumored that the Book of Returns to Tibet was written by the Yellow Emperor. With Kun as the first hexagram, it means "all things are hidden in it", but unfortunately died in the Wei and Jin dynasties. The bustling city is noisy even at night, the aunt carrying incense and candles in front of the bus stop, the snack seller who has no shadow under the street lamp, and the bear child who has to pester you to play a head-finding game with it...... There will always be someone who will travel through the dark and slay demons...... Casting out demons and guarding those who forget to sleep, these people are also known as night watchmen. Jiang Shiyuan, who just wants to live honestly and honestly in a stall under the overpass, was specially approved to join this organization that guards the night because he was too busy, and since then his life trajectory has come to a Thomas loop, which has become extremely fulfilling and thrilling. At first, when she knew that she was going to become a night watchman to stay up all night to solve the case, she refused until she found out...... The more bizarre and terrifying bloody truth behind the bizarre case. Looking at everyone's expectant eyes, she could only accept her fate and pick up the compass...... Wait, this last check came back to her?