Om Shakthi is a devotional drama built around the age-old belief that while human justice may fail, divine justice never does. Kathavarayan (played by Vijaykanth), the violent and arrogant son of a powerful landlord, rules the village through fear, exploiting the helpless and dishonouring innocent women. Unable to bear the shame and trauma, several victims take their own lives, leaving the village gripped by fear and silence. His cruelty reaches its peak when he sets his sights on Kannamma (played by Menaka), the virtuous daughter of a temple priest devoted to Goddess Shakthi.

As fear grips the village, faith becomes the only refuge for the oppressed. A righteous soldier Singaram (played by Jaishankar) returns home only to discover that his own sister, too, had fallen prey to Kathavarayan's brutality. As injustice reaches its peak, faith becomes the villagers' only refuge. In a mysterious turn of events, Kannamma's rooster Veeran starts to torment Kathavarayan.

When fate finally corners Kathavarayan, he is forced to face the consequences of his sins. In a powerful moment of reckoning at the feet of Goddess Shakthi, the tyrant realizes the weight of his crimes, proving the timeless truth.