 Na Du-su (Lee Seung-hyeon), nicknamed "Yalkae" (meaning "cheeky, cocky person"), is a 2nd grade high school student and a troublemaker.Together with Yong-ho (Jin Woo-young), they play pranks on their friends and teachers and neglect their studies, thereby earning a notorious reputation as "problem" students.One day, Du-su goes to his teacher Baek Sang-do's (Hah Myung-joong) boarding house for tuition and falls for In-suk (Kang Ju-hee), daughter of the grocery store owner from whom Mr. Baek rents a room.