Sanjay Singhania (Aamir Khan) is a rich tycoon suffering from short term memory loss due to being hit by a metal pole when trying to intervene on his girlfriend's murder. Because of the severe injury on his head, his memory can only last for fifteen minutes and he doesn't remember events or incidents that have happened before in his life. He can now only live a comprehendible life by tattooing notes on himself and taking pictures of things with a Polaroid camera to remind himself of the incidents that have happened. His story in unraveled by a police officer (Riyaz Khan) who is hunting him due to several murders he has committed while trying to find his girlfriend's murderer through his diary. His story has also piqued the interest of a medical college student, Chitra (Jiah Khan) who is searching for a patient with an "interesting" record for her college project. Chitra comes to know about Sanjay's love with Kalpana (Asin Thottumkal) a model cum activist. When her activist work for children comes in the way of child racketeers, she is killed by Lakshman when she intervened with his plan of kidnapping 25 young girls to Calcutta. So, with the help of Chitra, Sanjay sets out on a revenge spree, searching for the murderer of the one love of his life... The film's story revolves around a rich business entrepreneur falling in love with an ad film actress. The entrepreneur and the actress fall in love, though she does not know that he is an entrepreneur. When she successfully saves a bunch of children who were in danger, she is brutally murdered by a gang leader and the entrepreneur himself gets hit hard on the head when he tries to save his lover, eventually leading him into a state of short term memory loss. He is later studied about and helped by a psychology student to take revenge on the one who murdered his lover.