When a young gang leader seems to be just a bit too stupid to effectively carry out his daily tasks, his superiors order him to go back to school for his high school diploma. Posing as a 19-year-old, he soon learns that the school is even more corrupt and vicious. Wrath is unleashed.

Struggling artist Min Hee-do is offered three billion won to bet his life to a game against a rich old man, Kang No-sik, who is dying from a terminal illness. The game is for each man to dial a random phone number and guess if the person who answers will be male or female. Hee-do loses the bet, and after a month long brain operation, he wakes up to find that they have swapped bodies.

In his 10th year at college, Eun-sik is part of a nearly ideal campus couple with swimming champ Kyung-ah. While their three-year relationship is solid, Eun-sik struggles to get to the next level with Kyung-ah; despite the help and support of his friends, he can't manage to get her into bed.

Eun-sik tries to pass the state exam while studying in college after his military service. One day, he meets a beautiful woman Eun-hyo, and his life changes.