When an accident claims the life of her twin sister, So-yeon falls into a coma from which she awakes ten years later. However, a series of mysterious killings starts to take place upon her recovery, and she seemingly takes on her sisters personality traits. However, it is revealed that the one killed in the lake 10 years ago was not Hyo-jin but So-yeon and the living twin is truly Hyo-jin. The secret is hidden by her mother, who tells the villager that Hyo-jin is dead, but the dreadful spirit of Fake Hyo-jin (So-Yeon) comes back to take someone to live underwater with her.
Question: Who tells the villager that Hyo-jin is dead?, Answer: her mother Question: Who was really killed in the lake?, Answer: So-yeon Question: How long was So-yeon in a coma?, Answer: ten years