Five members of the mountain bike club, Sangaja. To ride a mountain bike, we head to Chiaksan Mountain, where Min-joon's Uncle villa is located. After arriving at Chiaksan Mountain and enjoying the ride, strange things began to happen to the party…. And something unidentified chasing them! A desperate survival game for Sangaja's party to survive on Chiaksan Mountain begins.

Jung-Woo (Kim Sung-Su) is a neurosurgeon and also works in bioengineering research. He is married, but has an ongoing relationship with Yoo-Gyeong (Han Go-Eun). She is a doctor and stands by Jung-Woo. Yoo-Gyeong has a mysterious accident one day and her hand is cut off in the accident. Thanks to Jung-Woo's quick thinking, her hand is reattached successfully with surgery. Yoo-Gyeong's health improves after the surgery, but bizarre events take place around her constantly.