The movie revolves around a family of four: A civil engineer father Shekar (Raghuvaran), the homemaker Chitra (Revathi), and two siblings, the elder brother Arjun (Tarun) and younger sister Anu (Shruti) both around II years old. Chitra had also given birth to a third child, but unfortunately, the girl was stillborn. About two years after the stillbirth, Shekar and his family move to a new apartment complex with many kids. The family seems to have recovered from the trauma and live happily. Overcoming the initial hiccups, the children make friends with many other kids living in the same complex and have a gala time playing pranks. On a New Year's Eve, while Shekhar is out on a business trip, Arjun slips out late at night with the older children of the locality to celebrate. He and other children are brought back home by the police. During this night out, Arjun had seen his father with another woman. When Shekhar reprimands him for leaving home at an odd time, Arjun blurts out that he had seen Shekhar with another lady. Shekhar denies this and scolds Arjun for telling a lie to save his skin.
When Chitra goes to meet Shekhar at his worksite without checking with him, she is surprised to learn that he had left the place citing some emergency at home. She gets suspicious, catches him redhanded walking with a lady, and confronts him. Not convinced with his explanation that she is just an acquaintance, she packs her bags to walk out of their home. Shekhar then confesses that their third child Anjali (Shamili) was born with several congenital complications and narrates the details.
The doctors had not given the child more than four days to live. To avoid the sorrow to an already physically exhausted Chitra and to protect his children from the trauma, he had colluded with the doctors to lie to his family that the child was stillborn. But much to the surprise of everyone, the child has made it past her second birthday and is seemingly physically healthy. The lady who was suspected to be Shekar's paramour is actually the doctor who is raising her. Though Chitra is sad about the truth being hidden from her, she decides to bring Anjali home.
Anjali is physically normal but mentally challenged. Shekhar and Chitra spend most of their time tending to her. Arjun and Anu initially get jealous of her and hate her. However, they slowly accept her after seeing her innocence and love. After initial hesitation, the kids of the locality too accept her and play with her, much to the annoyance of their parents. They call for a meeting of the residential association and the members advise the Shekhars, either to move out of the residential complex or send Anjali to an institution.
The only person who supports the Shekhars is an ex-convict (Prabhu) who is treated as an outcast by everyone. He becomes fond of Anjali who comes to meet him on her own. Shekhar witnesses a murder in his workplace and is prepared to come forward as a witness, so the murderer attempts to kill him. Prabhu comes to his rescue, kills the murderer, and goes to jail for the love he has for Anjali. The next morning, Anu goes to wake Anjali, but she doesn't respond. Anjali had died peacefully in her sleep. As more and more people come on hearing Anu's screams, they are saddened by the demise of the girl who taught them to love, accept, and forgive.
[from the book Pride of Tamil Cinema: 1931 to 2013, by G Dhananjayan, Blue Ocean Publishers, 2014]