A veteran female detective, So-Young, and her rookie assistant are investigating a recent series of bizarre murders. All of the victims seem to have died due to an acid unleashed inside of their bodies. As the two detectives discover more about their case, they soon start to realize that the recent serial killings may have something to do with a mysterious death that occurred ten years ago in a salt house. Soon, So-Young becomes plagued by nightmares in which the dead girl appears. And the killings continue.