"Kabhi Alvida Naa Kehna" (KANK) is the story of Dev and Maya, both married to different people and completely convinced that they are happy, until they meet each other. Dev (Shah Rukh Khan) is a professional soccer player whose promising career is nipped in the bud after an accident. He is married to Rhea (Preity Zinta) whose career is on an upswing. They have a son, Arjun, and Dev's mother Kamaljit lives with them. Maya (Rani Mukherji) teaches at a nursery and has married her closest friend Rishi (Abhishek Bachchan), a PR consultant. Rishi's father, Samarjit Singh aka Sam (Amitabh Bachchan) is a flamboyant, fun-loving man whose life revolves around the happiness of his son and daughter-in-law.

The two couples seem content despite the dissatisfaction below the surface but things start to change when a chance encounter between Dev and Maya brings them closer. There is a strange connection between them which blossoms into friendship.

Their time together soon causes complications. This new-found friendship between Dev and Maya causes them to look into their marriages with a new perspective and face up to issues that they hadn't before. How all the different characters deal with this new development in their lives forms the crux of "Kabhi Alvida Naa Kehna."