Take a nostalgic trip back to the late 1980s through the lives of five families and their five teenage kids living in a small neighbourhood in Seoul.

The arrival of an intimate letter prompts a young woman to bring her mother on vacation to a small Japanese town, where someone special resides.

Ean has a critical mission to return to the future to save everyone. However, she becomes trapped in the distant past while trying to prevent the escape of alien prisoners who are locked up in the bodies of humans. Meanwhile, Muruk, who helps Ean escape various predicaments, is unnerved when he begins sensing the presence of a strange being in his body. Traveling through the centuries, they are trying to prevent the explosion of the haava.

Ki-Chul drives his friends out to a resort situated by an abandoned coal mine. His father owns the resort. When they get there, they cross paths with a spooky man who warns them about the coal mine. Later, the friends find themselves in a desperate situation and enter the tunnels of the abandoned coal mine. Will they ever see the light of day again?