A sexual scandal between a math teacher and a student in a prestigious high school ended in tragedy. 4 years later they meet again, now as adults, to reveal the corruption in school and to regain one's reputation as a teacher.
Ji Yoon Soo is a high school math teacher with a bright smile and a positive impression of others. She is a hard-nosed and stubborn person who has to push ahead with the decisions she has made. She is a math geek who loves solving difficult problems and teaches students to purely love math.
Baek Seung Yoo is emotionless and has no light in his eyes. He used to be a math genius who appeared on a quiz program at the age of five and surprised the world by solving college-level math problems. He was admitted to MIT at the age of 10 but dropped out at the age of 12, and suddenly disappeared.
Lee Na Yeon is made an orphan when chaebol heiress, Park Yu Gyeong, causes the death of her mother, Lee Yu Nae, in a traffic accident. Yu Nae and Yu Gyeong had been rivals in love for the same man, Jang Gyeong Wan, with Yu Gyeong ensnaring him into marriage by claiming the child she is carrying is his. Jang attempts to make amends for abandoning his college sweetheart by trying to give the orphaned Nayeon a home, to the anger of Yu Gyeong and the jealousy of his daughter, Se Jin. When Na Yeon discovers evidence that her mother's death may be more than an accident, she forgoes the chance of a life of wealth and privilege for an orphanage. Taken in by the widow of the man who ran down her mother, Na Yeon grows up alongside Tae Jun, an impoverished but driven and academically brilliant young man who becomes the love of her life. However, he cheats on her for his own success and goes with Se Jin.
