Do Kyungsoo is nineteen and stuck in a mental hospital since the age of twelve. Let's just say 'Hey son, we're sending you to your grandparents for the summer' does not actually mean what you think it would, especially when summer means forever. Now Kyungsoo hasn't done anything wrong particularly, it's just how he behaves, more or less. Even though killing a few people might be pushing it a bit far. Now calling Kyungsoo a psychopath is acceptable to a certain extent, a mastermind is the correct term used to describe him. Everyone is frightened of Kyungsoo. In their words he's a hopeless case. The mark on his neck gives him the name 'Devil'. Reason being that the mark on his neck is actually the symbol of the devil. People have thought it is a tattoo, or it could have even been burnt onto his skin yet they won't accept the real fact that it just appeared on the three year old Kyungsoo's neck one day while he was out in the garden. Kyungsoo has escaped many a time from the hospital but he always been caught. What will happen when he runs into a man that he doesn't even know he met sixteen years ago. "Who are you?" "I'm your worst nightmare. I'm your best friend. I'm the devil."