Om Prakash “Omi” Makhija is a hopeful junior artist in Mumbai who dreams of true stardom. He shares a small home with his widowed mother, Bela Makhija, and his loyal friend Pappu Master in a cramped chawl. Omi is captivated by the glittering world of film and adores the glamorous Shantipriya, often venting his admiration in front of a life-size poster of the star. One night, he and Pappu sneak into the premiere of Shanti’s film Dreamy Girl, disguises and all, leaving a lasting impression on the actress. Later, in a drunken moment, Omi delivers a heartfelt acceptance speech to Pappu and local children, pretending to have won an award.
At R.C. Studios, Omi and Pappu land small roles under the gaze of the ambitious producer Mukesh Mehra, who also helped launch Shanti’s career. During a shoot, Shanti is trapped in a fire but is rescued by Omi, and the two form a tentative friendship. Omi initially pretends to be a Tamil film star to win her approval, but he eventually confesses the truth. Shanti genuinely likes him, and with Pappu’s help they share a quiet, memorable evening on the studio lot.
Omi overhears a heated argument between Shanti and Mukesh, revealing a secret: they are secretly married. Shanti reveals to Mukesh that she is pregnant with his child, a fact that seems to please him for the moment. Heartbreakingly, Omi withdraws, choosing to distance himself from Shanti.
The plot thickens when Mukesh takes Shanti to the future set of Om Shanti Om, claiming he will cancel the project and stage a grand wedding there to cement their union publicly. Omi visits Shanti and finds her with Mukesh, leaving both of them unseen by him as he departs. After Omi leaves, Mukesh exposes his true colors to Shanti—his plan is to murder her and their unborn child to secure his career. He sets the studio on fire and locks Shanti inside. Omi makes a failed attempt to rescue her, is beaten by Mukesh’s guards, and is eventually knocked aside by an explosion as the set burns with Shanti trapped inside. Omi is later struck by the car of Rajesh Kapoor, whose wife Lovely is in labor; Rajesh takes Omi to the hospital, but the injuries prove fatal for him, and Rajesh and Lovely welcome a baby boy named Om Kapoor.
Thirty years pass. Om Kapoor, also known as O.K., has become a successful but arrogant star who battles pyrophobia. Bela remains convinced that he is her son, while Pappu, now older, tries to help her see the truth, though Bela remains skeptical.
While shooting at the deserted RC Studios, O.K. experiences vivid flashbacks of Omi’s desperate attempts to save Shanti and even recites his old drunken Filmfare Awards speech on a television broadcast. Pappu watches and realizes that Omi has somehow reincarnated as Om Kapoor. At a party celebrating O.K.’s triumph, a chance encounter with Mukesh—now going by Mike—reawakens the old memories and prompts Om to confront the past.
O.K. reunites with Bela and Pappu at the old chawl, and together they hatch a plan to bring Mukesh’s misdeeds to light. He agrees to revive Om Shanti Om and, after many failed auditions, hires Sandhya “Sandy” Bansal, a young actress who is a perfect doppelganger of Shanti and a devoted fan of Om. Pappu and Bela begin training Sandy to behave exactly like Shanti. O.K. keeps his own plan close, but he shares the truth with Sandy, who vows to help.
At the film’s inauguration, Bela, disguised as a witch, and Sandy, disguised as Shanti’s ghost, attempt to intimidate Mukesh into confessing. A staged inauguration night goes awry, yet a photograph of Shanti somehow catches fire, unsettling Mukesh and sowing confusion among Om and Pappu.
During a masquerade ball for the music launch, Om hints at Mukesh’s guilt through Shanti’s story. Sandy’s unintentional slip reveals that she is not a real ghost, and Mukesh pursues her, only to be knocked unconscious by a falling chandelier. When he comes to, Om directly confronts him in the empty venue, insisting on the truth about Shanti’s murder. Mukesh taunts him, admitting that he knows Sandy isn’t Shanti. Then Sandy reveals that Mukesh buried Shanti alive under the chandelier after she survived the initial fire, and she even predicts that Shanti’s body will be found—proof of murder for the court. The confrontation leaves Mukesh unsettled, and Om, summoning the courage to overcome his fear, defeats Mukesh as the chandelier crashes down on him.
In the aftermath, Anwar arrives with the real Sandy and the truth is finally laid bare: the woman with Om is Shanti’s real ghost, who orchestrated the haunting to ensure justice. With Shanti’s spirit finally at peace, Om and Sandy reunite, Bela and Pappu share a quiet celebration of truth finally emerging, and Shanti ascends the stairs to vanish, having found her peace at last.
