Gurus in the late Goryeo dynasty try to obtain a fabled, holy sword, and humans in 2022 hunt down an alien prisoner that is locked in a human's body. The two parties cross paths when a time-traveling portal opens up.

Tae-jeo, a correctional officer with 15 years of experience, learns about the death of an inmate's mother during a night shift. On that winter night, she visits the funeral home and unexpectedly meets the inmate's daughter, Jun-young. Their encounter brings warmth to both their lives, and Tae-jeo hopes Jun-young understands: “Every decision you make shapes who you become."

Jay, a promising young writer, is about to publish her new book. Geonwoo, Jay′s roommate and lover, works as an English instructor at a private institute and silently assists Jay. Both of them care about each other and are happy as they are. However, Jay’s unplanned pregnancy brings huge changes, causing conflicts between the two.

Hee-jung hopes to leave Daegu and transfer to a university in Seoul. She works at a ticket office for paddle boats to save up for her tuition. One day while she dozes off, someone attempts suicide.