The story follows one serial killer who uses the help of innocent taxi drivers to murder his targets. When The Central Bureau of Investigation (CBI), India, has been made aware of a killer cab-driver in Malaysia who killed several people in a matter of hours and then crashed his taxi and killed himself. The same thing happened again, this time in Hong Kong, and several people were killed by another cab-driver, who also ended up being killed. Now, this time in Dubai, it is the turn of taxi driver Nikhil Joshi (Emraan Hashmi). Nikhil is an Indian living in Dubai for a good life and is madly in love with a cabaret dancer named Rhea (Nisha Kothari). He is willing to do anything for Rhea, and so is she. However, life has other plans for him when one night, a suave businessman named Vikram (Irrfan Khan) hails his cab.
Nikhil discovers that this pleasant passenger has an agenda of his own and a rather sinister one at that. Vikram holds Nikhil hostage in a bizarre plot to bump off various people who would testify against the dreaded don Jabbar (Zakir Hussain), who is at risk of being deported to India to face charges against him. As Nikhil helplessly becomes witness to one killing after another, he finds his life and dreams crumbling around him. He repeatedly pleads with Vikram to spare him and hire another taxi but fails. Faced with the prospect of losing everything he has been working towards, he finally takes control of the steering wheel of his life. He stops dreaming and starts acting, as he begins to pit his wits against the dangerous assassin.
Killing one after another, Nikhil seems to be the prime suspect, that's why Vikram plans to kill him in his taxi and flee, however, Nikhil fights back and dares Vikram by risking his life. After a series of murders of witnesses against Jabbar in the same night, the CBI officer and local Police Officer (Sanjay Batra) are closely on trail of Nikhil, who they assume to be The Killer. Nikhil destroys the laptop of Vikram, which contained the information of the witnesses in his hit-list. Vikram forces Nikhil to pose as Vikram and seek the particulars of the remaining two witnesses in the hit-list from Jabbar by meeting him personally in his mansion. Nikhil does so and procures the same and hands it over to Vikram, who had been waiting for him outside in the taxi. Nikhil decides to risk his life to save the witnesses and races his taxi to the horror of Vikram. The taxi hits a kiosk and crashes. Vikram runs off for his next prey, followed by Nikhil in the chase. He fails to save the witness, who is shot by Vikram. Nikhil sees his girl-friend Rhea's name and photo in the mobile, which fell off the fleeing Vikram. Determining to save Rhea from Vikram at any cost, Nikhil tries to contact her to warn her and flee, but her mobile gets discharged. He runs to warn her in the casino where she is dancing. The police and Vikram reach the place, and just as Vikram shoots at Rhea, Nikhil leaps and pushes her away. In the melee following the gun-shots, when the police confront Nikhil as the suspect Killer, he informs them that it is Vikram who is the actual Killer. He manages to escape from the place with Vikram in the chase after them. Finally, when Vikram confronts them and tries to shoot Rhea, Nikhil dares him to shoot him. The police shoot Vikram just as he is about to press the trigger of his gun. Thus Nikhil saves Rhea, and they are happily united.