Sharks don't have swim bladders, so they have to keep swimming to survive. This drama tells the story of the revenge of a man who is as terrible, pitiful and lonely as a shark. In high school, Zhao Haiyou, the daughter of a hotel group, and Han Yishu, the son of a driver, had an unforgettable first love. They had a common friend, Wu Junrong. Although Zhao Haiyou was born into a wealthy family, her family had many conflicts. Her father had an affair and her mother ran away. Han Yishu gave her great comfort and let her taste happiness for the first time. At this time, an accident happened, which brought it all to an abrupt end. Han Yishu's happy family was broken by the death of his father, and he soon realized that things were not simple. As time passed, Zhao Haiyou (played by Son Ye-jin), who had become a prosecutor, married Wu Junrong (played by Ha Seok-jin). On the day of the wedding, a mysterious man, Yoshimura Jun (played by Kim Nam-gil), appeared. This frosty man was the former Han Yishu. He changed his name and returned from Japan and appeared at the wedding scene, and the prelude to revenge was unveiled.