The film starts in the year 1990 when Iqbal Haroon Khan (Jackie Shroff) runs a circus – The Great Indian Circus – in Chicago, which has fallen on bad times. Anderson’s (Andrew Bicknell) bank – Western Bank of Chicago – which has lent money to Iqbal Khan, decides to close down the circus when he is unable to repay the loan. Young Sahir (Siddharth Nigam), the little son of Iqbal Khan, pleads with Anderson not to shut down his father’s circus as he and his father would soon be able to turn the corner. But Iqbal Khan’s presentation before the bankers and Sahir’s pleas don’t help. Iqbal Khan commits suicide in front of the heartless Anderson, leaving Sahir devastated.
Years later, Sahir (Aamir Khan) has still not forgotten the high-handedness of the bank and swears revenge. He robs various branches of Western Bank of Chicago, leaving behind a message in Hindi and a clown mask. He uses his acrobatic circus skills to escape. As Chicago Police Officer Victoria (Tabrett Bethell) failed to catch him, she calls ACP Jai Dixit (Abhishek Bachchan) and his partner, Ali (Uday Chopra), for help in solving the case. Jai baits Sahir into robbing again by making it known he’s on the case and he believes the thief is an amateur. Gathering information from a news channel regarding the plan, Sahir poses as an informant for Jai, and manages to gather information on the bank while giving Jai a lead to follow. Eventually, Sahir robs the bank and escapes, but Jai & Ali follow him. During the pursuit, Jai manages to shoot Sahir in the shoulder before he disappears again. Sahir has the big premiere of The Great Indian Circus with his female lead acrobat, Aaliya (Katrina Kaif), involving a trick with him disappearing in one place and showing up in another. The show is a success, but afterwards, Jai, Ali, and the police surround him, knowing he’s the thief. Jai says the proof is the gunshot wound Jai inflicted in Sahir, but when Sahir is examined, there is no evidence of a gunshot wound anywhere in his body. Jai & Ali leave while Sahir retires to his dressing room. It’s then revealed that Sahir has an autistic twin brother, Samar, who helps him pull off his trick and rob the banks, and it was Samar who sustained the gunshot wound.