This is a story of an orphan girl named Priya (Kareena Kapoor). Priya stays in Bombay but has come to Delhi as a transit student. Although an orphan Priya lives her life on her own terms. For a part time job she works as a choreographer's assistant. Her only dream in life is to find the right guy with whom she can have a small family that she never had. But she has a condition regarding the guy that she wants to marry. She wants some one who does not smoke, someone who doesn't drink and someone who never lies. Her friend's tease her saying that she is not looking for one guy, she is actually looking for three guys. Priya maintains a personal diary in which she regularly writes down her daily experiences.
One day Priya meets Sunita Rao, a very famous tarot card reader who is also the aunt of one of her best friends. Priya does not believe in fate, destiny and the fortune telling, but she is shocked when Sunita Rao tells Priya some very starting facts about her past life. Facts, which no one else knew except for her. Priya gets interested in knowing her future. Sunita Rao tells Priya that she will meet her life partner after seven days on a beach in South Africa. Priya is in doubt as there is no chance of her ever going to South Africa. Hence she takes the prediction with a pinch of salt.
Enters Amit (Shahid Kapoor), a young handsome guy. Amit is a chain smoker: he drinks and is the biggest liar of his college. As he goes to a different college he doesn't even know that some one like Priya even exists in Delhi.
Priya to her surprise discovers that she and her group have been selected to represent their college in a Youth Festival in South Africa. Priya is astonished at hearing this news as she feels that the Tarot Card reader's prediction has started to take shape.
On the other hand Amit who has not been selected to the same youth festival decides to go to South Africa with his friends on his own expense. Both Priya and Amit travel by the same flight but as fate would have it, do not see each other.
They land in South Africa at the youth festival, which is being held on a big Campus. That same night Amit who is trying to help one of his friends goes to the girl's dorm. He is spotted there by the matron and is chased by her. To hide from the matron he enters a room. This is Priya's room where she is fast asleep. Amit sees Priya and is mesmerized by her beauty. He finds Priya's personal diary at the bedside. He takes the diary and leaves the room. After reading the diary Amit gets to know all the likes and dislikes of Priya. He makes a Xerox copy of the diary and replaces the original. Thus from the next day he meets Priya and in a very humorous way convinces her that he is the life partner of her predictions. He even manages to make her believe that he is a non-smoker and a teetotaler, who never lies. Thus in the four days that they are at the campus, a relationship develops between the two. Priya falls madly in love with Amit, and he too starts feeling the same for her. But on the last day of their stay Priya comes to Amit's room and finds the Xerox copy of her personal diary. It dawns on her that Amit had been fooling her and that he is not at all the person who she believed that he is. Thus a confrontation follows between the two and Priya tells Amit that she will never ever meet him again.
While Amit tries to locate Priya and finally finds her, he says that it was destiny that made them meet. Right there Priya plays a destiny game with Amit, which goes on for years.
What is the destiny game, and how this love story unfolds is what Milenge Milenge about.