In 2006, the drug trade is booming. The Malaysian Intelligence and Anti-Narcotic Department are called upon for assistance by their Indian counterparts. There are rumours that a drug gang has recently moved their headquarters to Kuala Lumpur.
The Indian team is headed by DCP D'Silva (Boman Irani) who wants to break the back of the drug operations of a drug lord named Singhania. Also helping him is Malik (Om Puri). He believes that capturing Singania's dangerous and elusive lieutenant, Don, (Shahrukh Khan), will be the most effective way of accomplishing this. Don's gang consist of Narang (Pawan Malhotra) and Anita (Ishaa Koppikar). Soon, Roma (Priyanka Chopra) joins them but she has other plans - kill Don; Don was responsible for killing her brother Ramesh as well as his fiancee, Kamini (Kareena Kapoor).
During a chase with the police, Don is seriously injured and is captured by D'Silva. D'Silva keeps it a secret that he has captured Don, even from his fellow officers. D'Silva then proceeds to track down a Don look-alike, a singer named Vijay (also played by Shahrukh Khan). He asks Vijay to infiltrate Don's gang by pretending to be Don. In return he will make sure that the child Vijay found and adopted, Deepu, gets a proper education. Meanwhile, Deepu's real father Jasjit(Arjun Rampal) who has just been released from prison sets out in search for his son and to get his revenge on DCP D'Silva who arrested him and prevented him from rescuing his wife and child from blackmailers.