Shin Na Ra, a woman who is almost thirty welcomes her boyfriend of seven years back from his business trip. During their dinner, he tells her that he not only had an affair but fell in love with another woman. Thus their relationship is no more. To make herself feel better, Na Ra drinks a large amount of alcohol and unknowingly dropped the ring her ex-boyfriend gave her into a random stranger's cup. The stranger, In Jae, drinks the shot without seeing the ring and both of them end up in the hospital. To support herself, Na Ra pretends to be her 20 years old sister in order to work as a cosmetic clerk at Mi Rae (the woman her ex-boyfriend fell in love with)'s shop but fate has brought In Jae to the shop to. Thus began their surprising journey of love, where In Jae is in love with Mi Rae too.