Thamizh thug for hire in the city of Chennai who has no ties to anyone and will do any dirty work as long as the money as good. He meets a young girl named Shruthi and they fall in love. But there are two obstacles in the path of their romance : firstly, Shruthi detests Thamizh’s violent ways and secondly, police sub-inspector Govindan is pursuing Shruthi obsessively with intent of making her his mistress. Meanwhile, Dubai-based crime lord Ali Bhai has arrived in Chennai for the purpose of silencing his chief rival gangster Narasimhan and also to meet Thamizh who is rising within the gang’s ranks. However, during the meeting, Ali Bhai is arrested in a police raid conducted by Police Commissioner Mohammed Moideen Khan and his gang hatches a morally abhorrent plan in order to secure his release.
U.S.-based Bio-technologist, Govind K. Somaiyya, narrates from a stadium a tale of religious conflict in India – even before the appearance of Jesus and Allah. This conflict was between worshipers of Bhagwan Shri Shiv and Bhagwan Shri Vishnu – with devotees of the latter being put to death. Now in post-9/11 era President George W. Bush invests heavily in biological research but things get out of control when a vial containing a deadly chemical is inadvertently dispatched via courier to Tamil Nadu, India. In order to retrieve it, Govind must face heavy odds, including a deadly CIA Agent, Chris Fletcher; a killer named Jasmine; RAW Officer Pranab Kundu, as well as a martial-arts artist from Tokyo.
Spunky and compassionate Kalpana rents an apartment and works as an ad-model. Her life changes when she invents a love affair between herself and wealthy Sanjay Ramaswamy. When Sanjay finds out, he decides to confront her to end this facade, but ends up falling in love with her. He pretends to be poor, proposes to her, and she subsequently accepts. Before they could get married, she gets killed, Sanjay gets assaulted, resulting in memory loss, and he is unable to remember anything beyond 15 minutes. During those 15 minutes, Sanjay manages to put together bit by bit through tattoos, Polaroid photos, notes, and maps on the wall of his apartment whatever he is able to recollect, as he sets out to avenge Kalpana’s death. Sanjay does not know that the elusive killer knows about his agenda, and has already made plans to finish him off once and for all.
Medical student, Sunita, is driven by curiosity to study the case of Sanjay Singhania, who is afflicted with short-term memory loss. She runs into him, befriends him, and finds out that he is out to kill a seemingly benevolent citizen, Ghajini Dharmatma. After warning the latter of the impending danger, she subsequently comes across a number of diaries written by Sanjay and attempts to put together a jigsaw puzzle as to how a successful and wealthy businessman became a crazed recluse, who re-lives his past through tattoos on his body, notes and Polaroid photographs on the wall of his Hiranandani Complex flat, and his sole obsession of carrying out his deadly mission – little knowing that Ghajini and his goons are out to erase every bit of evidence he has gathered and thus ensure that he ends up remembering nothing.