The illegal drug trade based in Kuala Lumpur is booming. A team headed by Deputy Commissioner of Police De Silva (Boman Irani) is sent to Kuala Lumpur to target the operations of Singhania (Rajesh Khattar) and capture Singhania’s manager, “Don” (Shah Rukh Khan). Singhania is one of the two lieutenants of a deceased kingpin; the other is Vardhan, whose whereabouts are unknown.
After Don kills Ramesh (Diwakar Pundir), one of his close associates, Ramesh’s fiancée Kamini (Kareena Kapoor) decides to help the police, but she is also killed. Planning to avenge her brother and his fiancée, Roma (Priyanka Chopra) infiltrates Don’s gang. Don is injured and falls into a coma while trying to flee from the police. De Silva finds a look-alike named Vijay (Shah Rukh Khan) and asks him so the police can get close to Singhania. Vijay agrees when De Silva promises to admit Deepu (Tanay Chheda), a boy Vijay looks after, to a school in Kuala Lumpur. Meanwhile, Jasjit (Arjun Rampal), Deepu’s father, just released from prison, plans to kill De Silva.
Vijay is admitted to hospital, where Dr. Ashok Gilwani gives him scars identical to Don’s. When Don suddenly dies, the masquerade begins. Vijay, as Don, joins the gang in Kuala Lumpur. De Silva asks Vijay to find a computer disc containing details about the cartel and bring it to him. When Vijay finds it, Roma attempts to kill him, but De Silva tells her about his plan, and she agrees to help him. Vijay hands over the disc to De Silva. When De Silva murders Singhania, the police arrive and arrest Vijay. De Silva is killed in the shoot-out, which is unfortunate for Vijay because De Silva was the only person who could prove that he is not the real Don. Having discovered his true identity, Don’s associates turn against Vijay, but he escapes and, to prove his innocence, tries to recover the disc.