Karan Malhotra (Harman Baweja) is a spirited and happy-go-lucky boy who does not follow the rules. Sana (Priyanka Chopra) is the opposite of Karan: a sweet and shy girl who lives life by the rules. Even though they are completely opposite, they fall in love, leading to a magical love story. A scientist, Dr. Yatinder Khanna (Boman Irani), has dedicated 15 years of his life to building a time machine. Sana expresses a wish to time travel to Mumbai in the year 2050, but she is killed in an accident before her marriage to Karan. Karan wishes to travel back in time and find Sana. Dr. Yatinder, Karan, and Sanas siblings Rahul and Thea, travel forward in time and reach Mumbai, year 2050. They are fascinated by the futuristic Mumbai, withits flying cars, holograms, robots, 200-story buildings and more. Twists and turns lead to the introduction of Ziesha (Priyanka Chopra), the reincarnation of Sana. Ziesha is an popular singer in 2050 who does not remember her past life, but gets flashbacks of it after meeting Karan. Unlike Sana, Ziesha is an arrogant, headstrong and rebellious girl who does not believe in love. She leads a lonely life after the death of her parents, which has embittered her. Karan and the others find themselves under the threat of the demi-god, Dr. Hoshi. After Karan tells Ziesha he loves her, he is taken away from her by the guards. Ziesha does not believe him when he tells her about his time travel. However, after reading Sanas diary, Ziesha ultimately remembers her past life. Karan returns to her and she declares her love for him and tells him she is Sana. Dr. Hoshi tries to capture Karan because he wants the time machine. After a wild attempt to catch Karan and Ziesha, Hoshi crashes into a nuclear substance truck and dies. Karan goes back to 2008 in the time machine with Ziesha and the rest of his family. Everyone is overjoyed to see their beloved Sana again and Karan proposes to her.