Omkara or Omi (Ajay Devgan) is a gifted chieftain who heads a gang of outlaws, which include the crafty Langda Tyagi (Saif Ali Khan) and the dynamic Kesu (Vivek Oberoi) amongst his chief cohorts. The story begins when Omi appoints Kesu and not Langda as his chief lieutenant. Langda's pride is slighted and raging with envy he hatches a plot to falsely implicate Omi's beautiful lover Dolly (Kareena Kapoor), in a love affair with Omi's “favorite lieutenant”, Kesu.

With the unwitting aid of Indu (Konkana Sen Sharma), Langda's wife, and the willing help of Raju, a fellow grouch, Langda's plan takes shape and results in horrific tragedy. Using petty insinuations and lies, Langda keeps poisoning Omi's mind till one day it snaps and Omi goes about tearing up his own safe and secure world. By the time he realizes what he has done and the backlash of his actions it is too late…