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.
Jai is fired from the case, but is encouraged by Ali to prove Sahir's guilt by going rogue. Jai eventually finds out about Samar, and sets about finding a way to corner Sahir. Samar, kept in hiding and mentally challenged, is kept in seclusion by Sahir. However, Samar sneaks outdoor once a week, and Jai manages to befriend him during this time also manages to perform his plan. Samar has fallen in love with Aaliya after performing with her in the circus, but cannot express it. This leads to a rift between the brothers. Jai tries to take advantage of this, but Sahir finds out and thwarts Jai's plan to stop them. He decides the only way to catch the brothers is in the act. Sahir & Samar pull off their final bank heist, and escaped. However, the following day, Jai manages to corner them as they're making their way out of town. Samar is hesitant to run when Aaliya shows up, begging him to stop. Sahir surrenders to Jai, asking him to spare Samar and let him take the blame. Jai agrees, but right after, Sahir jumps off the bridge. Samar jumps, too, holding Sahir's hand refusing to let him go. Eventually, the two of them jump off the bridge together, apparently falling to their death. Finally Western Bank of Chicago is shut down as a result of the heists, while Aaliya is shown still performing for the Great Indian Circus. The film ends with the title song.