Writer Yudi (Saif Ali Khan) wrote a hit book five and a half years ago but he is still living life king-size in Los Angeles, enjoying fame and affairs, avoiding commitment, doing no work, partying with his miserably married friend Montu (Ranvir Shorey) or having conversations with his fat, bearded inner voice Yogi (also Saif). Suddenly, Yudi's money runs out and his publishers dump him for hit romance novelist Aanchal (Ileana D'Cruz), visiting from Mumbai.
The only work Yudi now gets is from Bollywood single-screen superstar Armaan (Govinda) who insists he copies Hollywood movies and writes a multiplex-style rom-comedy. Meanwhile, Yudi's dentist and once-girlfriend Vishakha (Kalki Koechlin) is pursuing him obsessively, even loading videos of him singing in the shower on her laptop, forcing Yudi and Montu to break into her home when she's away. On top of this, Yudi's got severe writer's block, stopping him from finishing any work.
Running away from it all, Yudi tries to charm Aanchal but she's commitment-averse too. However, she gradually warms up to him, escorting him to Armaan's party, trying to help Yudi write, even agreeing to take a road trip with him to her book reading in San Francisco. The duo has fun singing classic Bollywood numbers on the way until doziness overtakes them and their car skids. While they wait for the repair van, Yudi and Aanchal have a ball posing sexily on the highway in search of lifts.
Eventually reaching San Francisco, the couple is forced to share a hotel room – and agreeing to keep it simple and commitment-free, they end up making love. Their relationship grows funnier – on Aanchal's last night in LA, they argue over dinner, Yudi throws her phone into a vase while she douses him with water – but neither expresses anything more than a sense of light fun. It's only when Yudi's ex Divya (Priety Zinta in a cameo), having argued with her husband and visiting Yudi with her kids, tells him he loves Aanchal that he admits it to himself.
Yudi then races Aanchal's taxi to the airport in a hilarious scene and tells her his feelings – but she says, thanks, let's just be friends. As she leaves, Yudi's sunk in depression – and then starts to write. Along the way, Vishakha gets engaged to a panic-stricken Yudi by falsely claiming she's pregnant – but then breaks it up, saying she doesn't want him to marry her out of pity.
Armaan, who has meanwhile got himself cosmetic surgery and six-pack abs in LA, is impressed with the 'kick-ass' script Yudi presents him. However, for the script's ending, Yudi goes to Mumbai and sees Aanchal where he tells her they can take it one day at a time – and perhaps live their whole lives together like that. Aanchal smiles and the Happy Ending begins.
