The film opens with Akira (Anushka Sharma) swimming in a river. She suddenly starts sinking, prompting a passer-by Samar (Shahrukh Khan) to save her. Samar gives her his jacket to warm her. Akira thanks him and reaches her residence, to find out Samar's old diary which falls from the jacket's pocket. Curious, she starts reading it. Samar Anand in his late twenties lives in London, working as a musician. He also has a job as a part-time waiter in a hotel. One day, he meets Meera (Katrina Kaif) in her engagement party taking place at his hotel. Getting attracted to her, he meets her on a regular basis and starts falling in love. As time progresses, events take a turn as Samar is hit by a car and goes unconscious. Meera, who by-now reciprocates his feelings, start praying to god to save Samar and makes a vow to never meet Samar again. Soon, Samar makes a speedy recovery. Samar comes to know of this soon afterwards and in anger, tells her to go away and leaves London, giving all his money to his roommate. He goes to India and gets a job as an army officer posted in Kashmir.
As Akira finishes reading the diary, it is revealed that she works for the Discovery Channel and is in Kashmir to make a documentary on the bomb disposal squad of the Indian Army. She approaches Samar for his help and soon gets acquainted with him. She soon starts showing romantic feelings towards him, though he refuses a reciprocation due to his past. Akira makes the film successfully, earning her praise from the audience. She goes to London, after extensively persuading an overly hesitant Samar to come with her. In an unexpected accident, Samar again gets hit by a car and loses a large part of his memory, remembering only the events before his former accident. Akira meets Meera who now has a child to help her. After convincing her to act normally with Samar, the story continues as if Meera still loves Samar. Later, he comes across a bomb and diffuses it, with the result of his memory's return. In the end, Meera arrives at the scene. They reunite while Akira is shown addressing an audience in London, stating how Samar will be defusing his last bombs in India because there is a time for love, and the time for Samar and Meera's love is now.