Oldboy is about the idea that love conquers vengeance. It takes both of these concepts to their Shakespearean extremes and leaves them to duke it out in a fist fight to see which comes on top. Love does. Thus, love conquers vengeance. Signed, sealed, proven. Q.E.D. To hide the big twist of the movie, Oldboy starts out by pretending to be a revenge flick. The main revenge plot is that of Oh Daesu's quest to find the person who imprisoned him for 15 years and give him a piece of his mind. This revenge plot is supported by another revenge plot of Lee Woojin seeking revenge on Oh Daesu for having caused his sister's suicide. The love plot is the relationship between Oh Daesu and Mido. Which develops over the course of the story. In the end, Lee Woojin reveals that Oh Daesu had caused his sister's suicide by spreading a rumor about her love with Lee Woojin, and that he had sought revenge by imprisoning Oh Daesu for 15 years and setting him up to fall in love with Mido, who is actually his own daughter. So Oh Daesu is faced with a choice. He can kill Lee Woojin and win his revenge. Or he can apologize and try to preserve his love with Mido. In no uncertain terms, he apologizes. Love wins. The idea that love conquers vengeance is setup for a climactic clash clearly and dramatically. Then the idea is camouflaged with crazy high stakes, innovative directing and editing, a symphony orchestral sound track, and, of course, graphic Shakespearean violence that actually supports the story.