Three bachelors - Aroush (Akshay Kumar), Tanmay (Ritesh Deshmukh) and Ali (Fardeen Khan) are having the time of their lives in Sydney. They flirt around, sleep around and have numerous 'gorgeous' conquests to their credit. They suddenly find their dating and mating rituals irreparably destroyed when a dimpled little roommate lands up on their doorstep. Aroush, Tanmay and Ali know a thing or two about women, but when it comes to babies, they're total zeroes and this bouncing bundle of joy is anything but joyous. But then Angel works her charm and before long, the three lecherous bachelors have been tranformed into loving, caring fathers. But beautiful Esha (Vidya Balan) will have none of it. She has known heart break once and will do anything to avenge that betrayal and if it means breaking the hearts of three men who've finally discovered they possess one, then too bad.

Karan(Saif Ali Khan) meets Rhea(Rani Mukerji) in an aircraft, en route to U.S.A. They disagree on practically everything; they are complete opposites. So, to put things right, Karan innocently kisses her, which offends Rhea no end. The budding friendship ends in a disastrous note. Six months later, the duo meet once again in a park in New York. Rhea hasn't forgotten the kiss, Karan loses his girlfriend(Shenaz Treasurywala) in the process. Rhea and Karan continue to bump into each other at various phases of life and gradually become friends. Rhea goes through some personal tragedies in her life, but Karan stands by her. Karan even tries fixing her up with a friend of his Mihir(Jimmy Shergill) with her mother's(Kiron Kher) permission of course but as with everything else, even this doesn't work out. Instead, Mihir gets engaged to Karan's friend Diana(Isha Koppikar).

 But destiny has other plans for Karan and Rhea.