Ethirpaaraathathu narrates the story of star-crossed lovers Sundar (Sivaji Ganesan) and Sumathi (Padmini) in whose house Sundar, a college student, lodges. Both dream of a happy, married life, but that is not to be. Sundar is involved in an air crash and is believed to be dead. However, he survives the crash and loses his eyesight. Unwilling to face his father (Nagaiah), he tries to lead a life on his own. Destiny takes over their lives and the widowed father marries Sumathi and on the wedding night, the husband realises that his son and bride are sweethearts. Broken-hearted, he leaves home and wanders around visiting temples and holy places.
