I never made a review about a show before until now. this serie right here is one of the best psychological thriller series I saw. Koreans really do it the best and I mean it. the suspense, the build-up, the plot, the mystery, the characters, the acting, the camera work and the effects were immaculate. a big recommendation for people who love this genre like me and please watch it without knowing anything in advance. it will make the experience better and keep you up at night thinking. also you will feel all the emotions and it will raise a lot of philosophical ethical questions. honestly you can't stop yourself from crying during it and if you do you have a heart of steel. it's amazing so don't miss out on it.