Hyun-joo, a top-class student, suffers from emphysema. She wakes up one night, and is surprised to see some unknown black creature coming out from her nostril. In the morning, she finds out emphysema is magically gone. However, she is not as sharp as she used to be, and since that night, her exam scores get increasingly worse. Hyun-joo blames the black creature for all these changes, and she casts suspicion on So-young, her classmate who gives the answer to an unsolved question in class…