Plot
In 1977, Om Prakash "Omi" Makhija, a junior artist in Mumbai, dreams of becoming a renowned actor. He lives with his widowed mother, Bela, and his friend Pappu Master in a small chawl. Omi adores the glamorous superstar actress Shantipriya, often expressing his feelings in front of her film poster. One night, he and Pappu sneak into the premiere of Shanti's film, Dreamy Girl, in disguise, making a memorable impression on her. Later, Omi, inebriated, gives a heartfelt acceptance speech to Pappu and local children, pretending to have won an award.
Omi and Pappu land minor roles at R.C. Studios, owned by the egotistical producer Mukesh Mehra, who also launched Shanti's career. During a shoot, Shanti gets trapped in a fire but is rescued by Omi. The two become friends, and although Omi initially lies about being a Tamil film star to impress her, he eventually confesses the truth. Shanti grows close to Omi, and with Pappu's help, they share a memorable evening date together at the studio.
Omi overhears a heated argument between Shanti and Mukesh, revealing that they are secretly married. Shanti is furious when she learns that Mukesh plans to marry the daughter of the distributor for his upcoming film, Om Shanti Om. She reveals to Mukesh that she is pregnant with his child, which seems to please him. Heartbroken, Omi avoids Shanti.
One night, Mukesh takes Shanti to the future set of Om Shanti Om, claiming he will cancel the film and have a grand wedding there to make their marriage public. Omi visits Shanti but is devastated to see her with Mukesh; he leaves without either noticing. However, once Omi leaves, Mukesh reveals his true colours to Shanti, confessing that his actual plan is to kill her and their unborn child to avoid any impedance in his career as a producer. He lights up the set on fire and locks Shanti inside. Despite his attempts to rescue her after Mukesh leaves, Omi gets beaten by Mukesh's guards and is thrown out by an explosion by the time he can get to Shanti. The set burns down with Shanti inside. Omi is later struck by the car of actor Rajesh Kapoor, whose wife Lovely is in labor. Rajesh brings Omi to the hospital, but he dies from his injuries, while Rajesh and Lovely welcome a baby boy named Om Kapoor.
30 years later, Om Kapoor aka O. K., now a successful yet arrogant actor, suffers from pyrophobia and frequently encounters Bela, who believes him to be her son. He dismisses her as delusional, and Pappu, now old, tries to explain the truth, but Bela remains unconvinced.
While shooting at the abandoned R.C. Studios, O.K. experiences vivid flashbacks of Omi trying to rescue Shanti and later unwittingly delivers Omi's old drunken speech at a Filmfare Awards event. Pappu watches him on TV and realizes that Omi has reincarnated as Om Kapoor. At a party celebrating his victory, O.K. meets Mukesh, now known as Mike, who proposes a film collaboration; an introduction to him causes O.K. to fully remember his previous life. Om finally reunites with Bela and Pappu at the old chawl, and together with Om's assistant Anwar, they plan to expose Mukesh's crimes.
O.K. resumes filming Om Shanti Om at the old studio after convincing Mukesh to revive the project, and after many failed auditions of other actresses, hires Sandhya "Sandy" Bansal, an aspiring actress who is an exact doppelgänger of Shanti and a huge fangirl of Om. Pappu and Bela start training her to behave exactly like Shanti. Om initially hides his plan but later reveals the truth to Sandy, who promises to help him. At the film's inauguration, Bela, disguised as a witch, and Sandy, disguised as Shanti's ghost, try to scare Mukesh into confessing. Despite a fake inauguration plan gone wrong, a photograph of Shanti inexplicably catches fire, unsettling Mukesh and confusing Om and Pappu.
During a masquerade ball for the film's music launch, Om indirectly hints at Mukesh's guilt through Shanti's story. However, Sandy accidentally reveals her ruse by injuring herself, proving she is not a ghost. Mukesh, suspicious of the film reels, chases Sandy but is knocked out by a chandelier. When he regains consciousness, O.K. confronts him in the empty venue about Shanti's murder. Mukesh mocks O.K., claiming there is no proof and revealing he knows Sandy is not Shanti. Sandy then appears, disclosing that Mukesh had buried Shanti alive under the chandelier after discovering she had survived the initial fire. She even foretells that Shanti's body will be found, which will be proof of murder for the court. Both Om and Mukesh are perturbed at how deeply she knows Shanti's tragic story; in the confrontation that follows, Om finally overcomes his pyrophobia and defeats Mukesh, who is crushed to death by the falling chandelier.
Pappu and Anwar arrive with the real Sandy. Om then realizes that the woman with him is actually Shanti's ghost, who was also responsible for the unexplained aids in his plan. With her death now avenged, Om and Shanti bid each other a tearful goodbye, and he reunites with Sandy while Shanti runs up the stairs and disappears, having attained peace.
