

It is revealed that Sanjay is ultimately out to avenge the death of his sweetheart Kalpana (Asin), and that he is systematically killing the people who were responsible for it.

Sanjay uses a system of photographs, notes, and tattoos on his body to recover his memory after each cycle. It is revealed that Sanjay has anterograde amnesia where he loses his memory every 15 minutes. He takes a Polaroid picture of the man, and writes on it "done". Sanjay is introduced as he brutally murders a man. Sunita, nonetheless, decides to investigate the matter herself. Her professor denies access to Sanjay's records as it is currently under criminal investigation. She wants to investigate the curious case of Sanjay Singhania (Aamir Khan), a (former) notable city businessman, who is reported to have anterograde amnesia. The film opens with Sunita (Jiah Khan), a medical student, and her friends working on a project about the human brain.
