Eui-ju is a quiet student by day and a bold romance writer by night. Her future seems uncertain as the man she wronged becomes her homeroom teacher.

A sweet scene between teachers ignites Eui-ju's creativity. She casts them as leads in her new novel. During PE class, Gi-jeon makes her heart skip.

Eui-ju hides Woo-su's glasses after stepping on them by mistake. Given his demerits and tough task, she trashes them, thinking he's picking on her.

Once she realizes the glasses were special, Eui-ju digs them out of the trash but still gets a detention. She posts her F4-inspired web novel online.

"We Were Friends" goes viral. Riding the high, Eui-ju writes the steamiest cliffhanger yet, unaware someone is standing right behind her.

Woo-su demands she delete everything. Now forced to write the novel on his terms, Eui-ju hits a wall. Meanwhile, the principal has plans of her own.

On the EBC filming day, Da-ju urges Eui-ju to film Woo-su's class secretly, but she gets caught. She collapses and Woo-su carries her to the hospital.

Eui-ju wonders why Woo-su allows her to keep writing her novel. One offhand remark from him sets her heart racing.

As Eui-ju denies Woo-su's words made her flutter, a Fields Medal winner visits him. Misunderstood as liking Dong-ju, Eui-ju grows awkward with Go-ya.

Feeling inadequate, Eui-ju writes Deul-i as a villain in her novel. Woo-su considers a research proposal in the US, and the prospect makes Eui-ju sad.

Ji-a is captured by loan sharks. Woo-su gets in trouble trying to rescue her. Just as things look hopeless, someone arrives to save them both.

Dong-ju's secret is revealed. Eui-ju reconciles with Go-ya, and encouraged by her advice, decides to confess feelings.

Eui-ju's hesitant to confess. She realizes she's just a student to Woo-su. When Ha-su discovers her novel, her heart races with fear of being exposed.

The entire school finds out about the novel. Word reaches Young-hee, and Eui-ju must bring her parents to school. She tells her parents the truth.

Eui-ju is crushed after seeing how well Woo-su treats Deul-i at her guest lecture. After class, Eui-ju poses a life-defining math problem to Woo-su.

Eui-ju rushes to the hospital after hearing that Woo-su had eye surgery. She finally learns the truth behind the promise made ten years ago.