In 2018, the ranger team at Mount Jirisan is sent out to rescue a young boy as a typhoon approaches. While on the mission, Yi-Kang and Hyun-Jo discover a cave with a signaling system that Yi-Kang uses in 2020 to discover lost hikers.
2018: Yi-Kang puts an end to a potentially dangerous search for a missing lottery ticket. Hyun-Jo assists a man looking for a hiker who went missing a year earlier. Trouble ensues, so Yi-Kang comes to his aid. 2020: A ghost spots Da-Won.
2018: A young shaman tells Hyun-Jo that he will remain on the mountain even after he dies. After finding a dead hiker, Hyun-Jo informs Yi-Kang that he began to see visions of dead people on Jirisan after a soldier in his troop died there.
2020: While reviewing park records, Yi-Kang notices that Jo Dae-Jin had a day off each time someone died. 2018: Hyun-Jo has a vision in which a man with five scratch marks on his hand places a potato bomb that later kills a snake poacher.
2018: Hyun-Jo realizes that a potato bomb left on the mountain was intended to kill Yang-Sun. 2020: Yi-Kang informs Da-Won that she has returned to the park to find out who has been killing people since Se-Wook's death.
Christmas, 2018: Only Hyun-Jo and Yi-Kang are on duty at the ranger station. While she responds to a call about a hiker with an injured ankle during a snowstorm, he responds to a report that her first love has gone missing in the park.
2020: Da-Won spots Hyun-Jo's ghost on the mountain, even though he is still alive. Da-Won notices his ghost responds to Yi-Kang's voice. 2019: The ranger team responds to a forest fire in the park, during which Yi-Kang finds a skeleton.
2019: The rangers, police and fire department work to control the fire. The rangers try to rescue children trapped in a cave. 2020: While Da-Won is in the park, Yi-Kang learns that three people who have seen Hyun-Jo's ghost have died.
2020: Police question Dae-Jin in connection with Da-Won's death. 2019: The mountain spirit flag falls at the Mountain Spirit festival, which Yi-Kang's grandmother warns her is a bad omen. A hiker explores an abandoned village in the park.
1991: After the mayor of Black Bridge, a village within the park boundaries, refuses to allow a cable car project to be built, the village well is poisoned and villagers flee. 2019: Hyun-Jo and Yi-Kang look for a hiker near Black Bridge.
2020: Yi-Kang explains that Hyun-Jo was looking for evidence about the murders on the day that they were injured. 2019: Hyun-Jo learns that all the murder victims had a connection with the 1995 flood that killed Yi-Kang's parents.
2019: Torrential rain causes a flash flood and a landslide. The rangers head into the park to rescue stranded hikers. Yi-Kang meets a man who panics since he recalls that people who stayed in the shelter died during the 1995 flood.
2019: Yang-Sun falls into the water while attempting to rescue a hiker. Yi-Kang's grandmother dies after the bus on which she is riding plunges into a river. 2020: Hyun-Jo concludes that the murders are connected to Black Bridge village.
2020: Hyun-Jo's ghost meets Yi-Kang, telling her about the connection between Black Bridge village and the murders. Using his information, she sets a trap for the murderer, not aware that the murderer listened to their conversation.
2020: Hyun-Jo's family visits the park to commemorate him. With the help of Il-Hae, Goo-Young, and Dae-Jin, Yi-Kang pieces together what happened in Black Bridge village in 1991. She accuses Sol and Se-Wook of committing the murders.
2020: The rangers search the mountain for evidence that Sol has committed the murders. Yi-Kang remembers a crucial piece of evidence after reading a signal left by Hyun-Jo's ghost. Sol kidnaps Yi-Kang in order to kill her on the mountain.
