Medical scholar, 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 kind inhabitant or member, a person ‘with rights’, Ghajini Dharmatma.

After warning the laughter of the expected danger, she subsequently friend across a number of diaries written by Sanjay and attempts to put together a jigsaw something that puzzles as to how a successful and wealthy businessman became a insane person who lives alone and avoids people, who re-lives his past through tattoos on his body, notes and Polaroid photographs on the wall of his Hiranandani complicated flat, and his sunshine overwhelming preoccupation 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.