Set in New York City, the story of Kabhi Alvida Naa Kehna revolves around the budding romance between Dev Saran (Shahrukh Khan) and Maya Talwar (Rani Mukerji). The pair are unhappy in their separate marriages; Dev is married to Rhea (Preity Zinta) and Maya is married to Rishi (Abhishek Bachchan). Settled into a life of domestic ritual, and convinced that they are happy in their respective relationships; Dev and Maya still yearn for something deeper and more meaningful, which is precisely what they find in each other.

When Dev and Maya meet, the two realize that they complement each other perfectly. They fall in love with one another and begin to question the validity of their own respective marriages. The film explores the strong feelings that Dev and Maya have for each other, affect not only their lives, but also of those around them. From a relationship starting off in pleasant barbs the two begin to develop and acknowledge the feelings they have beneath the surface. When their feelings come to the fore, what results is a collision of lives and emotions, affecting everyone involved and changing them forever.