In Southeast Asia lies a mysterious island nation roughly the size of Singapore: Zelan Island. Shrouded in gray mist all year round, its black marshes spread unchecked. During World War II, the Japanese army established a secret laboratory here to conduct biological weapons experiments. Large amounts of chemical waste were left behind after the war, seeping into the marshes and causing living creatures to mutate. Thus was born the terrifying, gigantic, translucent eel known as the Mist Nightmare. The island's ecosystem suffered severe damage, and its trees and wildlife took on an eerie, dark hue.
The highest coastal peak, Mount Wuzuo, was named after the anti-Japanese hero Wuzuo. Its interior is riddled with karst caves and underground rivers. Once the heart of the Japanese army's laboratory, it has now become a forbidden zone for explorers, with rumors of mysterious creatures lurking there spreading without end.
Fifteen-year-old Chen Tian comes here on vacation with his parents. When his mother catches a cold, his father is kept busy caring for her, giving Chen Tian the chance to join an adventure. Seventeen-year-old Gao Yaying, a Chinese student studying abroad who is fascinated by the occult, arrives with fragments of a World War II Japanese army diary left behind by her father. Eighteen-year-old geology enthusiast Hua Yufu is skilled at making simple detectors, and discovers unusual metallic readings beneath the marsh. Twenty-year-old Nata, a member of an environmental organization, is secretly investigating the marsh's pollution. Three high school students have come on a graduation trip. They know Chen Tian from nowhere, but their shared thirst for exploration brings them together as an adventuring party. Nineteen-year-old Lin Yalan, the last member of the Lin family, runs the Wuzuo Mountain Resort on her own. She loves going barefoot and knows the terrain of Mount Wuzuo like the back of her hand. As they investigate deeper, the connection between the stench of dead fish in the marsh and the Japanese army's chemical waste, along with the truth behind the Mist Nightmare's mutation in Mount Wuzuo's caves, gradually comes to light.
