In Twin Secret, young doctor John hopes to build a successful medical career like his older brother. When he joins his brother's clinic, John faces unexpected challenges. His brother's wife, Mary, is a beautiful woman, always willing to help, and always seems closer than she should be. Meanwhile, her sister, Sabrina, seems intent on luring John into her trap, scheming and manipulating the young doctor. Twin Secret contains secrets that can only be revealed by reading a webtoon about the sexual adventures of a young doctor and two sisters.