Young-sun is a 15-year-old girl passionate about tennis. With no one to look after her, she moves between an orphanage and a shelter. To make her ends meet, she accepts a part-time position as Sua's training partner and later ends up living with her family. Other than their age, everything else was in stark contrast. Sua, coming from a wealthy family with a father who once was a tal-ented tennis player, receives special attention. Over time, Young-sun finds it difficult to conceal her envy towards Sua, who keeps acting childishly. Young-sun gradually begins to think of taking over what Sua has.