After a misunderstanding causes Do Kyungsoo causes her to fall out with her best friend and lose all her popularity, she ends up falling into the company of three outcasts including her former best friend and her first love, Kim Jongin.    

Despite being the only son of the most infamous Mafia boss in all of East Asia, all Do Kyungsoo wants is a regular school life without having one of his father's men watching him at all times. Enter Kim "Kai" Jongin, a broke teenage boy looking for a quick way to make money. Out of desperation, Kyungsoo's father hires him in secret to befriend his son and watch over him. Falling in love definitely hadn't been in the job description.