I watched this film not knowing anything about the plot. I think that was a good thing. The less you know the better in this case. If you are considering watching it, stop reading and just go, it's great. All I will tell you is that the movie is an excellent mystery thriller. While the themes can be violent or sad, it's not over the top or gratuitous. The impact comes from the way the story is revealed, piece by piece. The acting, I thought, was excellent. I only guessed one part of the mystery, otherwise the rest of the time I was glued trying to work out the answers. I know a film is good, when afterward I feel like the character were real, and this film gave me that sense of realism. A litte more character development and background would have been nice, as the pace gets going really early on. Otherwise fantastic Korean thriller that is well worth checking out.