It revolves around three roommates, Tashi (Imran Khan), Nitin Beri (Kunaal Roy Kapur) and Arup (Vir Das) leading an unkempt and debt-ridden life. Tashi's girlfriend Sonia (Shenaz Treasurywala) agrees to deliver a package for Vladimir Dragunsky (Kim Bodnia). Sonia then asks Tashi to deliver the package. Tashi, in turn, asks Nitin to do so. But Nitin is unable to do so as he is experiencing 'Delhi Belly'. The package keeps floating around and is finally handed to the recipient, a gangster named Somayajulu (Vijay Raaz) by Arup. Apart from the package, Arup also has to deliver a package which contains Nitin's stool sample to Nitin's doctor. He mixes up the two which makes Somayajulu furious and he starts the investigation by interrogating Vladimir. Meanwhile Nitin manages to photograph his landlord with a prostitute. He sends an envelope to his landlord which contains a copy of the photographs. Sonia is with Tashi when his co-journalist Menaka (Poorna Jagannathan) calls him for an important work. When he reaches the place he realizes that it is just a party and Menaka had called him just to have fun. Menaka's ex-husband Rajeev has an altercation with Tashi and hits him on the eye. Tashi retaliates and knocks Rajeev out. As Tashi and Menaka leave they are chased by a furious Rajeev and his friends. The duo barely manages to escape.
Vladimir informs Somayajulu that the mix-up must have been caused by Sonia as she didn't know what she was carrying in the package. Somayajulu calls Sonia, informs her about the mix-up and asks her to give him the address of the person who had delivered the package. When Tashi arrives at his apartment he notices that Somayajulu has taken the place under his control making Arup stand on a stool with his neck tied to a tie from the ceiling fan. On interrogating, Somayajulu discovers the location of his package.
Nitin gets the package from his doctor's office which Somayajulu snatches and opens. Inside it are thirty diamonds. He examines them and orders his men to kill everyone. One of them pushes the stool on which Arup was standing. The other one gets ready to kill Tashi. Meanwhile, the fan to which Arup was tied falls down along with the ceiling and injures most of Somayajulu's men. Tashi, Arup and Nitin escape along with the diamonds and spend the night at Maneka's place. The next day they sell the diamonds to a local jewellery shop owner. They celebrate their good fortune which is cut short by Somayajulu's call saying if he doesn't get his diamonds back, he will kill Sonia. The trio, feeling disgusted, goes to get the diamonds from the jewellery shop owner, only to be told that they will have to pay him double.
The trio starts worrying when Tashi comes up with a plan. Nitin, Arup, Tashi and Maneka disguise themselves in burqa and go to the jewellery shop. They con the owner, take back their diamonds and return his money. They then go to the hotel where Sonia is held by Somayajulu. On the other hand the police is after Tashi's car. Tashi, Arup and Nitin reach the hotel room and see Sonia. They ask Somayajulu to take the diamonds and leave her. Meanwhile the police arrive at the hotel room and start shooting. Somayajulu and his gangsters fire in return.
In the end, only Nitin, Arup, Tashi and Sonia survive the gunfight. Menaka is upset to learn about Tashi's engagement and leaves him. Tashi breaks off his engagement to Sonia. Later it is revealed that Nitin managed to keep the real cash with him while duping the jewellery shop owner. The film ends when Menaka comes over to Tashi's to hand over his car's wheel cover lost while escaping from Rajeev. Tashi manages to jump into her car through the open window and kisses her.