Song JiHyo and Jay Park are best friends, and lived a life full of violence. In short, they are cold-blooded killers who know nothing about emotions and feelings. There is a reason for all this. At a young age, they were kidnapped by two people, and when they were saved, they swore to exact revenge on the two of them. How? Their targets were their children. However, things start to go wrong when they are introduced to emotions they have never experienced before. One of them being Love.