Finally, Seung Yoo and Yoon Su reveal the secrets behind Asung Academy and Noh Jung Ah to the world. How will Noh Jung Ah's defeat look? What will become of Seung Yoo and Yoon Su's relationship? The final story will be much more beautiful than the love of mathematics the two share.
Seung Yoo and Yoon Su finally reveal the truth behind the scandal that happened in their past. While Noh Jung Ah puts forward a scapegoat after getting cornered, Ye Rin begins to crumble in her anxiety and despair. Meanwhile, Yoon Su, who now can smile like Seung Yoo always wanted, chooses to be in the position to protect Seung Yoo.
Yoon Su starts to smile little by little thanks to Seung Yoo, and the two of them have an enjoyable and memorable time together. Meanwhile, Noh Jung Ah, who is furious at Yoon Su for targeting her, decides to get in the way of Si An, the one student Yoon Su cherishes. Yoon Su notices the provocation and resolves to face her.
Seung Yoo tries to bring Yoon Su out into the world from her rut by getting close to her heart, just the way she helped him. Meanwhile, Yoon Su keeps her identity hidden while collecting evidence of Noh Jung Ah's corruption. However, when Yoon Su's identity is in danger of getting exposed, Seung Yoo stands in front of her.
Now that he has reunited with Yoon Su, Seung Yoo tries to get close to her again. Noh Jung Ah, who doesn't know that Yoon Su has become an elite instructor at an academy, asks the academy for the guidance of her daughter, Ji Na. Meanwhile, Sung Jae appears in front of Seung Yoo and Yoon Su, who are together.
After four years, Seung Yoo has now become a renowned mathematician, and he returns to look for traces of Yoon Su who has disappeared after the incident in 2017. Meanwhile, Principal Noh Jung Ah of Asung High School of Math and Arts proposes an offer to Seung Yoo, and Seung Yoo responds with another offer.
Seung Yoo and Ye Rin prepare in earnest for the Math Olympics. Jung Ah and Min Jun teach Ye Rin the means to win, and Yoon Su finds out about the corruption in the competition. However, Yoon Su goes to Jeju Island with Seung Yoo to help him with the contest. On the same day, Ye Rin arrives at Jeju Island for internship activities for the competition.
At Asung High, Yoon Su’s new workplace, she gives a tricky question for students who want to join the math club. While no one in the class got the question right, a correct answer sheet is posted on the board outside the classroom. To find out who did it, Yoon Su provokes them and manages to find who it is.