In 1989, Ponni, a hardworking police constable without real higher-life aspirations, aims to ensure that her daughter Dhanam receives a good education and becomes a responsible person.

Maari, Ponni's husband and a mill worker, aspires to break free from rampant caste issues and poverty in their village by getting involved in local elections.

When Maari returns the next day to apologise and get his job back, Perumal, the mill owner, and his relatives, driven by their senseless casteism and misogyny, humiliate him and make derogatory remarks about Ponni.

When Ponni seeks justice for Maari and Dhanam's deaths in court, the culprits use their influence and receive a minor sentence.

Sangayya reconciles with Ponni due to a similar incident in his past and how he formed a close bond with Dhanam.

During this time, Perumal is hunted by his younger brother Giri, who was also in charge of helping the group hide in different areas, due to an inheritance dispute and lost his life.

Sangayya insists on Ponni to protect Sudalai since Giri will arrive to kill his nephew to eliminate the last remaining heir to the mill and the properties left by his grandfather.

Sangayya sacrifices himself by blowing up the van after lighting up several gas cylinders, which he had stowed inside, killing the reinforcements as well as Giri, thus leaving Ponni devastated.

[8] Ashameera Aiyappan of Firstpost rated the film 3/5 stars and wrote "Saani Kaayidham is a solid revenge drama that achieves its humble aspirations".

[9] Janani K of India Today rated the film 3/5 stars and wrote "Saani Kaayidham is a neat revenge thriller which lacks depth in writing.

[11] Latha Srinivasan wrote in Moneycontrol that “Saani Kaayidam' rests firmly on the shoulders of Keerthy Suresh and Selvaraghavan, and works to a great extent only because of them.”[12] Haricharan Pudipeddi of Hindustan Times stated "The film pushes Keerthy Suresh out of her comfort zone while Selvaraghavan contributes in not making the film end up as a blood-soaked tale of vengeance".

Saani Khaayidham tries to deviate from that, but ends up reinforcing another trope - that a woman, who is otherwise primarily the wife, daughter, or mother, needs to go through something as traumatic as a sexual assault to become “stronger”.

[14] Srivatsan S of The Hindu wrote "Filmmaker Arun Matheswaran’s second instalment in what he calls his ‘revenge trilogy’ is gory and disturbing.