Bewafaa tells the love story of two person between Anjali (Kareena Kapoor) and Raja (Akshay Khumar). Anjali lives in Montreal, Canada with her parents. She meets with a young man named Raja, and both fall in love. When Anjali's India-based married sister, Aarti Sahai, comes for a visit she takes her to be introduced to Raja, and Aarti approves of him. Raja is also introduced to the family, and there is all-round approval.

Then Aarti gets pregnant, tragically passes away, after giving birth to twin daughters, which results in a crisis in the family. This crisis is resolved when Anjali is asked to marry Aarti's businessman husband, Aditya, in accordance with Hindu traditions. Fearing that the twins will be neglected and harmed if Aditya re-marries someone else, she consents, and a quiet marriage ceremony takes place, and thereafter they relocate to India with the twins.

Years pass by, Aditya is engrossed in his business, and has no time for Aarti, who yearns for his company and makes every attempt to be a good wife, going to the extent of trying to look exactly like Anjali, and to please him. However, Raja shows no signs of affection. And then Raja comes to India for a tour, meets with a much more subdued and mature Aarti - and they rekindle old flames - only to run into an angry Aditya and his friends - who will do their best to prevent Aarti from getting back with Raja.