Kindhearted girl Cha Eun-hye transfers to a big city. Her brother, Cha In-jun, warns her to be wary of bad boys, especially handsome and wealthy ones. Cha Eun-hye knows her first rule as an adult is to stay away from her brother's rival, Park Sung-hoon. However, inexperienced in romance, she can't resist Park Sung-hoon's advances, and he, in turn, is puzzled by her immunity to his charms.