The story follows Aarush, (Akshay Kumar), a jinxed loser who stays with his friend, Bob (Ritesh Deshmukh) and his wife, Hetal (Lara Dutta), both working at a casino owned by Mr.Kishore Samtani (Randhir Kapoor). Although at first Hetal is displeased with Aarush's presence, he proves to be a kind-hearted man looking for family. Bob and Hetal decide to get him married to their boss' daughter, Devika Samtani (Jiah Khan). After the marriage, on their honeymoon in Italy, Devika leaves him for her long-time American boyfriend Benny. Aarush decides to commit suicide by drowning in the sea but is saved by a Telugu girl Sandy (Deepika Padukone).
Sandy originally thinks Aarush is a pervert, but when Aakhri Pasta (Chunkey Pandey), the owner of Italy's biggest hotel where Aarush was spending his honeymoon with Devika, tells Sandy that Aarush is a widower, she befriends him and slowly falls in love with him. What she doesn't know, is that Aakhri Pasta was only joking. She then finds out his wife is alive and leaves him, but when he tries to make her understand, she accepts him.
The only way Aarush can get married to Sandy is by convincing her elder brother, Major Krishna Rao (Arjun Rampal), a strict INDIAN MILITARY INTELLIGENCE officer who loves and is over-protective of Sandy. Meanwhile, Hetal lies to her father, Batuk Patel (Boman Irani), that Bob owns a mansion and they have a child. The four rent a mansion to make him believe that Bob owns it, but Batuk accidentally believes that Aarush is married to Hetal, and Bob is the cook. Then, Krishna turns up, much to Aarush's horror, leading to more lies.
For half of the term, the four must pretend that the mansion is owned by Bob, and the rest must pretend that Aarush owns it. An overly suspicious Krishna sees Bob and Hetal working at the casino and uses a lie detector to find the truth. After Sandy objects, Krishna apologises and agrees to Aarush & Sandy's marriage. The whole family is invited to the Royal Palace, to see Krishna get rewarded by the Queen of England. While this is happening, 2 workers are meant to be installing air conditioning gas for the place, however instead they accidentally supply the hall with laughing gas causing everyone to break into an outburst of laughter. During this laughter, the truth is let out but no one seems to be in the right state of mind.
The 2 workers meanwhile stop the gas from spreading – everyone comes back to their senses. Aarush is still telling Krishna the truth, leading Krishna to break off Sandy's engagement. However, after Sandy tearfully pleads with him, Krishna lets the two get married. In the end, Hetal and Bob live together with Batuk Patel, and Aarush's luck changes for the better.
