Minyoung and Howon have been best friends since they were babies,they grew up together and now live together after the sudden loss of Howon's parents.When they were in elementry school they promised they won't fall in love with anyone but each other,little did they know Myungsoo was going to ruin that promise.

Howon has eyes for Minyoung and only Minyoung but what will happen when she grows fawn of her lab partner Myungsoo and decides she will  'give her heart' to him after one month. Just like the good gentle men his mother raised him to be he accepts it and tells Minyoung she should go for it even though he knows what Myungsoo really thinks about her.