The film is based on the legend of the Lake Tianchi Monster in Changbai Mountains. It tells about the scientific expedition led by Zhong Wenshan in 1955 to look for the strange disappearance of the water monster. There is an underground river connected to another mysterious place under the water. Every 24 years, the water level drops and the underwater hole will be exposed. For this reason, according to the guidance of Zhong's father's diary, everyone entered an untouched primitive jungle through the mysterious cave in the thick fog. There is no signal, the magnetic field is disordered, and the beautiful appearance is full of dangers. A deadly worm that lurks underground and cannibalize people at any time