The police are baffled by a master theif known only as Mr. A (Hrithik Roshan) because he leaves an 'A' symbol after each robbery. Mr. A steals the crown jewels of a queen by sky diving onto the train carrying them, and then disguising himself as the queen and as usual escapes the authorities.
Meanwhile Ali (Uday Chopra) who is now a officer fouls up a mission and is narrowly saved by ACP Jai Dixit (Abhishek Bachchan). They soon meet ACP Shonali Bose (Bipasha Basu), who has been assigned to solve the case of Mr. A. Shonali and Jai are ex-classmates. Their apparant flirting makes Jai's wife Sweety (Rimi Sen) jealous. Ali promises to help her by wooing Shonali. While reviewing Mr. A's crimes, Jai realises that Mr. A is actually challenging everyone to catch him. His next theft will be in Mumbai.
There are two places where he might strike, A jewellery shop, and a museum. Jai and Shonali stake out the jeweller while Ali stakes out the museum. Jai realises that Mr. A will rob the museum after learning that the supposed target of Mr. A is damaged. Mr. A manages to make his escape by roller-blading and using a magnetic device. Shonali is disheartened that Mr. A escaped and decides to resign. Mr.A is planning to leave the city, but at the airport he learns that someone else, using his name has announced that he will rob the sword kept in the Junagadh fort. Mr. A decides ro meet the imposter. The imposter turns out to be Sunehri (Aishwarya Rai), who confesses that she is a fan of Mr. A and would like to be his partner. Mr. A is doubtful at first, but later he agrees. But Sunehri is actually working for Jai Dixit.
Mr. A takes Sunehri to Rio de Janeiro to train her and also for their next heist. Jai and Ali follow them to Rio, where they meet Shonali's twin sister Monali (Bipasha Basu). Monali takes a liking to Ali. Mr. A finds out that Sunehri is working against him. After he confronts her, Sunehri decides to stop betraying him and work with him. Their robbery is successful.
There follows a high-speed bike chase, ending with Mr. A and Jai fighting on a waterfall. Ali manages to capture Sunehri, to stop Mr. A. Sunehri shoots Mr.A so that he is not arrested by the police. Jai lets Sunehri go free, deeming it punishment for her to live alone. Six months later, Sunehri and Mr. A are shown running a restaurant, but Jai follows Sunehri and finds Mr. A. Jai lets them both go when Mr. A gives him a list of all the heists he was planning to do.