|Samar Anand (Shahrukh Khan), a major in the Indian Army, defuses a bomb showing no fear or regard for personal safety. After a while, Akira Rai (Anushka Sharma), a Discovery Channel filmmaker, dives into a river in Ladakh and is rescued by the major. Samar gives her his jacket but leaves before retrieving it. Akira finds his diary in the jacket pocket and starts reading.
The diary recounts Samar's earlier years as a struggling immigrant in London. He worked as a musician and found other menial jobs to support him and his roommate. One day Samar is offered work as a part-time waiter where he meets Meera (Katrina Kaif) during her engagement party. In exchange for English lessons, Samar agrees to teach her how to sing. In the process, Samar and Meera fall in love. On the day Meera is supposed to tell her father about their relationship, Samar gets into a terrible accident. Meera prays to God to save his life and makes a vow to never meet him again. Soon Samar makes a speedy recovery and comes to know about the vow. In anger he tells her to go away and leaves London. Samar challenges God to keep him alive while he will risk his life everyday because he believes his death is the only way to make Meera lose her faith in the deity who stole his love. He goes to India and enlists in the Indian Army.
As Akira finishes reading the diary, she requests her supervisor to make a documentary about a bomb disposal squad and is granted permission. She approaches Samar for help and soon gets acquainted with him and his team. She starts showing romantic feelings towards Samar but he refuses to reciprocate due to his past. Akira makes the film successfully and departs for London, earning praise for her work. To launch the film, she needs Samar to visit the city. After she extensively tries to persuade a reluctant Samar, he finally agrees to come to London, but is hit by a car upon arrival.
Samar is diagnosed with retrograde amnesia, remembering only the events before his first accident a decade years ago. Akira tracks down Meera and persuades her to aid in Samar's recovery. Meera agrees and pretends to be Samar's wife. During this time, Akira realizes that Major Samar is only a fragment of the young Samar. He used to be a jubilant social man but is now a bitter lonely individual. One day Samar comes across a bomb planted in the London Underground and helps defuse it. This event triggers his memory and he realizes Meera was lying to him. Samar confronts Meera and gives her a choice, either be with him or he will keep on risking his life until he is dead. Samar departs for Kashmir where he continues defusing bombs. During a conversation with Akira, Meera realizes that her beliefs and prayers subjected Samar to a fate worse than death. Meera, realizing her mistake, travels to Kashmir where they reunite. Samar defuses his last bomb and proposes to her on the spot.