South of the Sun is a love story between Kang Sung-jae (Choi Min Soo), who has been in prison despite his innocence and cut off from the world, and Jung Yeun-hee (Choi Myung Gil), who appears to be happy on the surface but is suffering from isolation. They find each other through a letter by coincidence and madly falls in love after finding out the loneliness they share equally. But when ex-fiancé of Sun-jae, Min-joo, reappears in Sung-jae’s life, they face conflict.