Bang Bang story begins with Harleen Kaur (katrina) who works as a receptionist at a bank. In an attempt to find an alliance, she goes on a blind date and chances upon Rajveer (hrithik) who is extremely charming yet mysterious. In fact, Rajveer is a secret agent on a mission. Situation turns such that Harleen has no choice but to stick with Rajveer and she also discovers his true identity. What happens after that forms the rest.