Eight years ago, the youngest daughter, Gyeong-ju, disappeared during a school field trip to Gyeongju and never came home alive. On what would have been her birthday, her mother Ok-sil and her three daughters—Jang-ju, Young-ju, and Dong-ju—put on matching family T-shirts and set off for Gyeongju, the place where Gyeong-ju vanished, in what appears to be a family trip to honor her memory. But beneath the cheerful façade lies a deadly secret. In the trunk of their van is a bound and unconscious man zipped inside a plastic bag.

An incident unfolds when a film crew goes to a reservoir to update the road view where an unidentified figure was filmed, and they encounter something in the dark, deep waters.