Kang Hyun Se grew up without knowing his father. Due to the lack of fatherly love, he was recruited by a gang and became a third rate mobster. After his mother's death, he inherits a kindergarden, but he must go through a hundred days of training in order to get it, so he becomes an assistant teacher under a kindergarden teacher Yoo Mi Rae and they develop romantic feelings for one another. However, the kindergarden property sits in the middle of an proposed amusement park development, called "Rainbow Park". Hyun Se's boss needs the money from the construction company so he is manipulating Hyun Se's hatred towards his father and threatens Hyun Se's father with the kindergarden Hyun Se has. Little does Hyun Se know that Choi Shi Wan, who is the ex-boyfriend of Yoo Mi Rae, struck a dirty deal with Hyun Se's boss and is trying to outscore everyone.