Young Raj Malhotra (Akshay Kumar) lives with his elder brother, Rohit, his sister-in-law, Kiran, and his niece. After an accident fractures his leg, he is unable to walk for some time. Due to psychological reasons, he cannot walk even after the fracture heals. When the Malhotras move to Dehra Dun, Raj befriends their neighbour, young tomboy Kajal (Lara Dutta), as both share a common passion for aeroplanes. Kajal encourages Raj to walk, and he succeeds. Years later the two continue to be fast friends, and everyone expects them to marry soon. Raj secretly loves Kajal and is waiting for the right time to propose to her. However, Kajal sees him only as her best friend. Raj is recruited by the Indian Air Force and goes for training for a year and a half. After his training is over, he rushes to Kajal to propose to her, only to find out that she is in love with multimillionaire businessman, Karan Singhania (Aman Verma). Raj tells Kajal that Karan is the best life partner for her, and does not reveal his true feelings. Kajal and Karan get married and during the reception party, Kajal comes to know of Raj's feelings for her. Hurt by the fact that she did not see his feelings for her despite being Raj's best friend, Kajal asks him to move on with his life. Thereafter the Malhotras move to Nainital, and Raj relocates to Cape Town, South Africa for training.
During a visit to a club, Raj meets the vivacious and fun-loving Jiya (Priyanka Chopra). Jiya falls in love with Raj due to his clean personality, but Raj is unable to forget Kajal. After completing his training, Raj goes back to India where he finds that Jiya has already arrived and is living as a paying guest with his family. Jiya makes several attempts to impress Raj, however he still doesn't fall for her. During Karva Chauth, Jiya performs the rituals that a wife typically does for a husband but Raj becomes angry and asks Jiya to leave. Raj's family reveals that they had hoped Raj would marry Jiya. Finally, Raj gives in and decides to marry Jiya and move on with his life.
While visiting Jiya's family, Raj learns that Kajal is Jiya's sister-in-law. It is revealed that Kajal is now a widow after Karan's death in a plane crash, in which Kajal survived. Kajal blames herself for Karan's death and even attempts suicide. Raj helps Kajal recover from her depression and enables her to face life again. Jiya notices their increasing closeness and suggests to her father that Kajal be married off. At Raj and Jiya's engagement, Kajal comes to know that her family has arranged her for engagement as well. Raj asks Kajal not to allow herself to be married off against her will. Angrily, Jiya states that Raj and Kajal will never be able to forget their past love for each other, regardless of the fact that Raj is supposed to be marrying Jiya. An irate Raj places the wedding sindoor on Kajal's head, indicating he has now married Kajal and no one has the right to question their relationship. Emotionally, Jiya reveals that she wanted Raj and Kajal to accept their feelings for each other in front of the world. The film ends with Jiya participating in Raj and Kajal's wedding ceremony.