Prem's (Ranbir Kapoor) fundas in life were very simple - be happy...make others happy...keep the town happy... But these supposedly simple fundas usually results in disastrous consequences for Prem, the members of his Happy Club, and the town!

It may have been a case of mistaken identity that led Prem to kidnap Jenny (Katrina Kaif). And it was sheer greed that made Prem try to pull a fast one over her father. As for sweet and simple Jenny, brought up by indifferent and uncaring foster parents, all she longed was to love and be loved in return.

And it was love and only love for Jenny that made Prem turn over a new leaf. From hardly working vagabond he began working hard to make money... From a besotted Romeo, he becomes a mature and thoughtful Majnu who put Jenny's happiness above everything else...As for Jenny...she was so much in love with the idea of being in love that she was blinded by the reality that was staring in her face…