Min Jae lives with his mother in Seoul as his father moved to Daegu due to his office relocation. He starts suspecting his mother to have an affair with someone else. Seo Yeon lives with her mother, who split up with her father, and they are on bad terms. Her mother takes her to a gynecologist.

Min Jae takes expensive private math tutoring. He goes to Daegu to see if his mother visits his father. He runs into Seo Yeon on the train back to Seoul. An official ID card is issued to Gi Hyun, Min Jae's friend, as he turns 17. Min Jae's math tutor promises to award Min Jae if he gets' Grade 1 in the next exam.

Seo Yeon has dinner with her mother and her mother's boyfriend, who gets her a grand piano. Min Jae quits tutoring as his tutor calls Seo Yeon a nasty and crappy girl. Min Jae runs into Seo Yeon when she is about to meet a guy for compensated dating. The photo of Min Jae and Seo Yeon in front of a motel is posted on Yakjin High's Anonymous Secrets, the school's web page.

After fighting with Gi Hyun, Min Jae has an argument with Seo Yeon at school. Seo Yeon visits her father's wedding alone and meets her father's stepdaughter Mi Ju. Min Jae witnesses his mother seeing her boyfriend. Min Jae and Seo Yeon share and talk about the pain they suffer and comfort each other.