Seung-yoo and Ye-rin prepare in earnest for the Math Olympics. Jung-ah and Min-joon teach Ye-rin the means to win, and Yoon-soo finds out about the corruption in the competition. However, Yoon-soo 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. Who will win the battle?