An Affair is a psychological thriller film directed by Rupert Wyatt. The movie revolves around a young teacher named Hae-il (played by Lee Dong-Gun) who starts to notice that one of her students, a teenage boy named Seong-hyeon (played by Ye Ji-won), is following her every move. Initially, Hae-il tries to ignore Seong-hyeon's behavior, but as time passes, she becomes increasingly disturbed by his obsession.
As the story progresses, Hae-il's personal life begins to unravel. She suspects that her husband is having an affair, and her health starts to fail due to the stress of her situation. Meanwhile, Seong-hyeon's behavior becomes more and more erratic, and Hae-il realizes that he may be dangerous.
The movie explores themes of obsession, revenge, and the blurred lines between love and hate. It is a tense and suspenseful film that keeps the audience guessing until the very end. The performances of the actors are pitch-perfect, particularly Ye Ji-won, who delivers a chilling performance as the disturbed teenage student. Overall, An Affair is a gripping and thought-provoking thriller that is sure to leave viewers on the edge of their seats.