This show embraces the tv trope that serial killers are like mice - if you see one, there's another dozen living in the walls of your house that you haven't seen yet. But that device can probably be forgiven thanks to the absolutely chilling and wonderful performances by Park Bo Gum and D.O. in their respective roles. Jang Na Ra and Seo In Guk were also delightful in this series. Very little was as straight forward as it might seem, so the twists were genuinely interesting. There are also some lapses of logic in the scripting that one could drive a homicidal box truck through, but most of those are pretty early on so you get over them and get to move on. :) The ending is an emotional roller coaster. I definitely now want to see Park Bo Gum in something where he's not flat affect and uber creepy. I don't know about rewatch value on this. The performances were engaging, but with the plot already laid out and the twists already known, I'm not sure that it would have as much impact the second time around.