Mann is a story about Karan Dev Singh (Aamir Khan) who is a young flamboyant playboy and uses every trick in the book to charm wealthy women, who will shower him with expensive gifts and support his extravagant lifestyle. There is only one problem though. Karan is always looking for greener pastures, at the same time when is already engaged to marry a billionaire's daughter to ensure a free flow of money for life. At this point in the movie he is travelling from Singapore to Bombay aboard a ship to go back to his fiancée.
Mann is also the story of Priya (Manisha Koirala) who is also travelling on the same ship to Bombay, on her way to marry her fiancée.
Karan continues with his philandering ways and sets out to charm and add Priya to his list of conquests. However, after being snubbed by her, he is enamoured by her disarming nature and withdraws his advances, surprising even himself.
Both Karan and Priya try to distance themselves from each other and sail back to their respective to-be spouses. But it's too late, cupid has struck and they are already in love with each other.
The struggle for the future (Karan, for the first time would have to start to earn a living - Priya, an orphan, indebted to her fiancée for being there for her) represents a challenge, which they deem to be the course of their lives.
Karan and Priya decide to meet at a pre-designated place only after a period of 6 months to start their life together.
Do they meet? If they do, do they unite? Is Karan really up to changing his ways? Does Priya have the moral courage to defy her fiancee's selfless love for her?
Mann is film about...listening to your heart.