Synopsis: Omkara Shukla or Omi (Ajay Devgn) is a bahubali, a sort of political enforcer. He is the leader of a gang which commits political crimes for the local politician Tiwari Bhaisaab (Naseeruddin Shah). Ishwar 'Langda' Tyagi (Saif Ali Khan) and Keshav 'Kesu Firangi' Upadhyaya (Vivek Oberoi) are his closest lieutenants.
The movie starts with Langda Tyagi gate-crashing a baraat and challenging Rajju (Deepak Dobriyal), the bridegroom, to try and stop Omkara from abducting the bride, Dolly Mishra (Kareena Kapoor). Rajju fails and the wedding never takes place.
Dolly’s father Advocate Raghunath Mishra (Kamal Tiwari), mostly referred in the movie as vakeel saab (lawyer sir), is furious and confronts Omi. He puts a gun to Omi’s head and demands the return of his daughter. Bhaisaab intervenes and resolves the conflict by mentioning the current political conditions and prevents bloodshed. Still unconvinced, Raghunath grieves to Bhaisaab the next day. To bring an end to this issue, Dolly is made to appear in front of her father and clarify that she eloped with Omi and was not abducted. She also tells the events of how she fell in love with Omkara. The father leaves feeling betrayed and ashamed. The director here references one of the most significant lines of the play Othello, with Dolly's father repeating the couplet almost verbatim, albeit in translation. The original lines read, "Look to her, Moor, if thou hast eyes to see. She has deceived her father and may thee."
After some crafty political arm-twisting, involving an MMS sex scandal, Omkara eliminates a powerful electoral rival. Bhaisaab is elected for parliament and Omkara is promoted from bahubali to the candidate for the upcoming state elections. Omkara appoints Kesu over Langda as his successor once he enters politics himself. Langda, disappointed with Omkara's poor judgment and jealous of Kesu, his younger, less-experienced, superior, hatches a plot to avenge both his offenders. He first causes a violent brawl between Kesu and Rajju by taking advantage of Kesu's low threshold for alcohol. Such irresponsible behaviour by Kesu infuriates Omi, who now starts having doubts over his decision.
On the one hand, playing the role of a concerned friend, Langda convinces Kesu to appeal to Dolly, Omi's lover and newly wedded wife, to mollify Omi. On the other hand, he starts to disrepute Dolly by implicating Kesu's visits to her as an illicit affair between the two. A kamarbandh carelessly dropped by Dolly and stolen by Langda’s wife Indu (Konkona Sen Sharma), which eventually reaches Billo Chamanbahar (Bipasha Basu) as a gift from Kesu, plays an important part in the plot, as evidence of Dolly’s infidelity.
During the climax, on the night of their wedding, Omi is convinced that Dolly and Kesu have been having an affair behind his back. In rage, he smothers his new wife to death. Langda shoots Kesu with a silent approval from Omi. Kesu is hit with a bullet on his arm. Hearing gunshots and in shock, Indu enters the room where Omi is sitting next to Dolly’s corpse in remorse. Indu notices the kamarbandh and confesses to stealing it; they both understand the fatal misunderstanding with Langda as its root cause.
In retribution, Indu slashes Langda's throat and Omi commits suicide. The movie closes with Omi lying dead on the floor and Dolly’s dead body swinging above him, while Kesu looks on.