Samar Anand (Shahrukh Khan) is a poor musician in London. He soon meets Meera Thapar (Katrina Kaif) and is instantly attracted to her. He soon learns that Meera is engaged to marry a childhood friend. However, Samar and Meera start spending time together and Meera realizes that she is also in love with Samar. At the same time, Meera realizes that she cannot be with him because of her engagement. She and Samar make a mutual agreement that they shall not cross the line of friendship, but break this agreement. Tragedy strikes when Samar meets with an accident and is injured badly. Meera soon tells Samar that she believes she cannot love him anymore and tells him to leave her life. Samar does so and decides to join the Indian army as a bomb diffuser. 10 years pass, Samar is now a Major in the Indian army. When he saves the life of Akira Rai (Anushka Sharma), she finds his diary, in which he wrote about his love story with Meera. Akira is fascinated with Samar and decides to make a documentary about his life in the army. Akira then shifts to London and Samar soon joins her. However, Samar has another accident, and this time he develops retrograde amnesia. He keeps thinking he is still in his life with Meera. Akira decides to bring Meera back to Samar, hoping it will help him bring regain his memory.