Dong Hae was raised in America by his beautiful but unmarried and mentally deficient mother who was adopted there. He returns to Korea with his mother because of the woman he loves, but she betrays him. Dong Hae begins to search for his father, creating a new family and finding new romance along the way.

Kim Sun Kyung is a retired police officer and father of three sons, Gun Kang, Hyun Chal and Yi Sang.

His eldest son Gun Kang made many wrong decisions in life, ending up being divorced and going bankrupt. Gun Kang gets remarried to Chung Nan. His second son Hyun Chal is the envy of the town and pride of his father. He runs a number of businesses which are quite successful. His wife Woo Mi often sacrificed her happiness for the benefit of the Kim family. As for the last son Yi Sang, he follows in his father's footsteps by becoming a police officer. Oftentimes the father and the son clash each other. As Yi Sang married Eo Young, the daughter of his father's deadly foe, an ex-convict Sun Kyung traced and eventually arrested a long time ago.

"Three brothers" revolves around their relations full of conflicts and love.

Jung Ha Yoon is a graduate student who successfully passed the bar exam. However, she is not finished as she wants to be a medical malpractice litigation specialist. She works at a hospital to look to gain experience and there she meets other doctors who work there.