Kim Haneul is a four years old kid of a workaholic CEO named Kim Jongin and a designer mother, Jung Hyori. The family were so happy until her father cheated on her mother, Until her father divorced with her mother and got married with his girlfriend. Now that she lives with her mother. Her mother looks happy but she knows she is not really happy. 

One day when she woke up in the middle of the night, she saw her mother crying silently on her room and it brokes her heart. The next day, she asks her mother if she can spend the day with her father. To make her father see how sad her mother is because he left her.