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.

Were they happy? And were their lives beautiful?After the death of his mom, Ji-hoon (Go Soo) moves into the home of Mr. Suh. Ji-hoon falls in love at first sight with Mr. Suh's daughter, In-hye (Park Jung-ah). Ji-hoon also becomes good friends with Suk-hyun (Bae Su-bin) But one day, In-hye decides to leave home for Seoul to pursue her dream of becoming an accomplished cellist, without telling Ji-hoon. Suk-hyun also decides to move to Seoul after he learns that he is the love child of President Kang, a wealthy hotel magnate.When Ji-hoon finds out that In-hye left for Seoul without even saying goodbye, he finds his way to Seoul to find her. One day, while Ji-hoon is riding the subway, Jung-woo (Park Ye-jin) takes a liking to him and decides to steal his wallet to get his attention. Through this incident, Ji-hoon gets to know Jung-woo and settles down in Seoul by enrolling in the same bodyguard school that Jung-woo is attending. The bodyguard training school finds a part-time job for Ji-hoon and Jung-woo, which is an assignment to guard President Kang for one day. Ji-hoon protects President Kang at an evening party hosted by Kang himself, and by coincidence, he also meets In-hye and Suk-hyun. The fates of four young people become hopelessly intertwined after this fateful meeting.