Song Joong-ki, an optimistic young man in his 20s who works various part-time jobs to support his second sister (Lee Yun-eun) and third brother (Jungkook) with a different surname, has a huge revenge plan hidden in his heart. On the day when my sister Yun En reported to Hongda, all the planning started quietly. The three people had a clear division of labor and a tacit understanding of cooperation. Things progressed as they expected. Those who framed the three parents back then were all punished as they deserved. However, the perfect plan went awry. People can never accurately control their emotions. Song Joong-ki, who used the principal's daughter (Kim So-hyun), found that he was gradually moved by her kindness and simplicity, and often hesitated in the execution of certain actions. And the second sister Li Yunen met the sunny and handsome senior Nam Joo Hyuk from the physical education department in school, and she helped him escape from difficulties many times. She also gradually discovered that Jungkook's feelings for her were unusual. The frozen hearts of the three people who came together for revenge were gradually melted by something after the revenge plan was launched. They were conflicted and entangled. What should they do when facing the last remaining target of revenge?