Former agent Chu Huan (played by Chen Xingxu) accidentally fell off a cliff after successfully chasing the leader of the drug cartel “大鬼”. He stumbled to a small county town with serious injuries, where he met two strange people who healed his injuries..After that, the two took him back to the mountains and asked him to teach the children in the mountains. Chu Huan unexpectedly discovered that the children here were extremely powerful and brave, and there was something strange about the mountain as well.These “mountain guards” in the mountains cannot step out of the “river” boundary to the world of ordinary people for most of the year, but there is an opportunity once a year for the mountain gate to turn upside down, so Chu Huan made up his mind to take advantage of the mountain gate.On the day when Reverse was about to leave the mountain guardian's residence, an accident happened, which also brought about a strange adventure.