Every morning, Sanjay is reminded by a tattoo on his body that "Kalpana was killed", and it is revealed that Sanjay is ultimately out to avenge Kalpana, and that he is systematically killing the people who were responsible for Kalpana's death. His main target, evidenced by several notes and tattoos, is "Ghajini". It is eventually revealed that Ghajini is a notable social personality in the city. Mumbai Police Inpsector Fawaz is on the case of the serial murders. He tracks Sanjay down to his flat and attacks and disables him.

Through a 2005 diary found in the room, Fawaz learns Sanjay Singhania is the scion of a reputed business house that owns the Air Voice mobile telephone company. In the course of his business, Sanjay sends his men to meet Kalpana, a struggling actor/model, about putting up an Air Voice billboard above her apartment. The owner of Kalpana's modeling/advertising firm misinterprets this as a romantic advance, and encourages Kalpana to accept the advance.

Kalpana plays as Sanjay's girlfriend. He eventually meets Kalpana, but pretends to be Sachin, a simple fellow from a small town. Kalpana lands him some modeling gigs. They fall in love, and on the New Year's eve, Sanjay proposes. She requests some time to. Sanjay decides that if she accepts, he will tell her who he really is, but if she declines, he'll quietly back off with no harm done. He finally tracks down Ghajini to a college function where Ghajini is the guest of honor. Sanjay takes some pictures of Ghajini and decides to kill him.

Later that evening, Sanjay attacks and kills one of Ghajini's goons in the parking lot. The dying goon informs Ghajini that Sanjay is out to kill Ghajini. Ghajini is baffled about the identity of the person and decides to eliminate all his enemies. In the meantime, Sunita who he met at the party visits Sanjay's flat and finds detective Fawaz, beaten and bound. She also finds that Ghajini is Sanjay's target. Fawaz informs her that Sanjay is a known serial murderer. Sunita finds the two diaries and frees Fawaz. Sanjay arrives suddenly and in the ensuing chase, Fawaz is fatally hit by a bus, and Sunita barely escapes the crazed Sanjay.

Believing Ghajini is in danger, she informs him that it is Sanjay who is after him. With this named target, Ghajini arrives at Sanjay's flat and destroys all the photographs and notes, and tattooes over Sanjay's existing tattoos. Satisfied that he has neutralized Sanjay by wiping out any trace that connects back to him, Ghajini leaves.

Meanwhile, back in her dorm, Sunita reads the 2006 diary ,which revealed that Kalpana had accepted Sanjay's proposal and ends abruptly. Sunita investigates further, and discovers that at some point in 2006, Kalpana had rescued 25 girls from a prostitution racket. The girls named Ghajini as the ringleader of the racket. In retaliation, he murdered two of these girls, and went in search of Kalpana. Ghajini and his goons managed to break into Kalpana's apartment and waited for her return.

Coincidentally, Sanjay also arrived there to meet Kalpana. Her last word to him was "Ghajini." Ghajini kills Kalpana and hits Sanjay in the head leading to his memory loss. Sunita, now aware of the truth, finds Sanjay and tells him the truth. Arriving at Ghajini's lair in downtown Mumbai, Sanjay systematically and brutally kills all of Ghajini's henchmen and chases down Ghajini. He is about to kill Ghajini when his memory loss cycle kicks in. Ghajini takes this opportunity to stab Sanjay. He begins to taunt Sanjay with the grisly tale of how he murdered Kalpana. Sanjay, angered by this devastating memory takes out the sharp pole in his stomach and throws it at Ghajini,which knocks him to the floor. Sanjay overpowers Ghajini after a short fight and kills him in the same way Kalpana was killed. The film ends with Sanjay, still suffering from the amnesia, volunteering at an orphange. Sunita gives him a small gift, a memorabilia containing both of their footprints literally to remind him of his fond association with Kalpana

Ghajini opens with Sunita, who is investigating case of Sanjay Singhania, who is a notable city businessman, reported to be suffering from amnesia in spite of being denied by her professor. Sanjay is introduced as he's murdering another man and takes the picture of the corpse. The amnesia he has wipes his memory out every 15 minutes. Sanjay uses a system of photographs, notes, and tattoos on his body to recover his memory after each cycle. Every morning, Sanjay is reminded by a tattoo on his body that "Kalpana was killed", and it is revealed that Sanjay is ultimately out to avenge Kalpana, and that he is systematically killing the people who were responsible for Kalpana's death. His main target, evidenced by several notes and tattoos, is "Ghajini". It is eventually revealed that Ghajini is a notable social personality in the city. Mumbai Police Inspector Fawaz is on the case of the serial murders. He tracks Sanjay down to his flat and attacks and disables him. Through a 2005 diary found in the room, Fawaz learns Sanjay Singhania is the scion of a reputed business house that owns the Air Voice mobile telephone company. In the course of his business, Sanjay sends his men to meet Kalpana, a struggling actor/model, about putting up an Air Voice billboard above her apartment. The owner of Kalpana's modeling/advertising firm misinterprets this as a romantic advance, and encourages Kalpana to accept the advance. Kalpana plays as Sanjay's girlfriend. He eventually meets Kalpana, but pretends to be Sachin, a simple fellow from a small town. Kalpana lands him some modeling gigs. They fall in love, and on the New Year's Eve, Sanjay proposes. She requests some time to. Sanjay decides that if she accepts, he will tell her who he really is, but if she declines, he'll quietly back off with no harm done. He finally tracks down Ghajini to a college function where Ghajini is the guest of honor.

Sanjay takes some pictures of Ghajini and decides to kill him. Later that evening, Sanjay attacks and kills one of Ghajini's goons in the parking lot. The dying goon informs Ghajini that Sanjay is out to kill Ghajini. Ghajini is baffled about the identity of the person and decides to eliminate all his enemies. In the meantime, Sunita who he met at the party visits Sanjay's flat and finds detective Fawaz, beaten and bound. She also finds that Ghajini is Sanjay's target. Fawaz informs her that Sanjay is a known serial murderer. Sunita finds the two diaries and frees Fawaz. Sanjay arrives suddenly and in the ensuing chase, Fawaz is fatally hit by a bus, and Sunita barely escapes the crazed Sanjay.

Believing Ghajini is in danger, she informs him that it is Sanjay who is after him. With this named target, Ghajini arrives at Sanjay's flat and destroys all the photographs and notes, and tattooes over Sanjay's existing tattoos. Satisfied that he has neutralized Sanjay by wiping out any trace that connects back to him, Ghajini leaves. Meanwhile, back in her dorm, Sunita reads the 2006 diary ,which revealed that Kalpana had accepted Sanjay's proposal and ends abruptly. Sunita investigates further, and discovers that at some point in 2006, Kalpana had rescued 25 girls from a prostitution racket. The girls named Ghajini as the ringleader of the racket. In retaliation, he murdered two of these girls, and went in search of Kalpana. Ghajini and his goons managed to break into Kalpana's apartment and waited for her return.

Coincidentally, Sanjay also arrived there to meet Kalpana. Her last word to him was "Ghajini." Ghajini kills Kalpana and hits Sanjay in the head leading to his memory loss. Sunita, now aware of the truth, finds Sanjay and tells him the truth. Arriving at Ghajini's lair in downtown Mumbai, Sanjay systematically and brutally kills all of Ghajini's henchmen and chases down Ghajini. He is about to kill Ghajini when his memory loss cycle kicks in. Ghajini takes this opportunity to stab Sanjay. He begins to taunt Sanjay with the grisly tale of how he murdered Kalpana. Sanjay, angered by this devastating memory takes out the sharp pole in his stomach and throws it at Ghajini,which knocks him to the floor. Sanjay overpowers Ghajini after a short fight and kills him in the same way Kalpana was killed. The film ends with Sanjay, still suffering from the amnesia, volunteering at an orphange. Sunita gives him a small gift,a memorabilia containing both of their footprints literally to remind him of his fond association with Kalpana.