Scarlet Innocence is the love story of a teacher and a student 17 years younger than him, from a forbidden love with many infatuations, madness, jealousy gradually with misunderstandings turned it into hatred and resentment. The film begins with a literature teacher at a prestigious university in the city, but a sex scandal caused the handsome guy Hak-kyu (Jung Woo Sung), who already had a daughter, to transfer to a school in the countryside.
Meanwhile, 20-year-old female student Deo-kee (Som E.) suddenly finds life more interesting than ever since she met Hak-kyu, who in fact only sees her as a passing love to solve the emptiness in the new working environment. The mutual attraction leads the couple to passionate moments but when the fall semester begins, Hakkyu has to return to his family in the city. He wanted to end his relationship with Deokee, but she refused as love meant the world to her.
From there, their confrontation turned into tragedy when Hakkyu’s wife committed suicide. 8 years later, Hak-kyu became blind and estranged from his daughter, Chungee. At this time, he befriended a new neighbor named Se-jung. She offered to help him and he happily accepted, from which Chungee became attached to her, and neither of them realized that Se-jung was actually Deokee and she was looking for the right time to take revenge…