After a stormy romance, Tanu (Kangana) weds Manu (R. Madhavan). But four years later, living in London, the romance between the two has died. The couple complain bitterly about each other to marriage counsellors and Manu, who’s a doctor, gets so enraged, the counsellors suspect his mental state and put him in custody.
Tanu goes back to their flat but is lonely and bored. Her friend Payal (Swara Bhaskar) calls her from India and confides that her newborn baby is not actually born of her husband Jassi (Eijaz Khan). Tanu is amused and decides to return to her hometown, Kanpur. Before leaving London, Tanu rings Manu’s buddy Pappi (Deepak Dobriyal) in Delhi and tells him to come to London, to have Manu released from the mental asylum.
Reaching Kanpur, Tanu lights up the town, having once been its heart-throb. Even Deepak, the local rickshaw-puller, has a crush on her which she indulges. In her parents’ home, Tanu finds a crafty law student, Chintu (Mohammad Zeeshan Ayyub), has become a lodger who refuses to pay or leave. Chintu develops a crush on Tanu and she befriends him, going about Kanpur with him. Tanu even dresses in a towel and shocks people meeting her sister for marriage. She visits Raja Awasthi (Jimmy Shergill), her gangster-turned-contractor ex, but he tells her he’s getting engaged to a nice girl soon. Tanu wishes him well and leaves. Chintu snidely tells Raja he is supporting Tanu through her turmoil in the hope of having some fun but Raja cautions him to behave properly.
Meanwhile, Pappi is enjoying the sights in London when Tanu scolds him and he rushes to get Manu out. Manu and he leave for India where Manu is morose and tells his parents he wants a divorce. Manu’s mother nags constantly while his father says everyone in a marriage suffers. Manu sends Tanu a warning legal notice but she doesn’t respond.
Manu goes to Delhi University to give a medical talk but he sees Kusum (Kangana), a young Haryanvi student-athlete, who looks like Tanu. Manu makes Pappi complete the talk (with hilarious results) and rushes off behind Kusum, whom he collides with at a race track. Pappi feigns a heart attack to escape the lecture and tells Manu not to keep following Kusum, she’s just a lookalike and will get them beaten up. But Manu is obsessed.
Kusum notices Manu following her and confronts him, hitting him with her hockey stick. When he tells her she resembles his ex-wife, she sympathises and they become friends – and slowly, more. When Kusum backs off and says her sister-in-law has arranged her marriage already, Manu tells Kusum he wants to marry her and meets Omi, her elder brother. Omi has no issues with Manu but shows a picture of the boy his wife wanted Kusum to marry – Raja Awasthi.
Meanwhile, Chintu is jealous of Raja going around with Tanu and tells her father about it. Chintu even sends Manu a nasty legal notice for a divorce, without Tanu’s consent, but Manu responds by agreeing, which shocks Tanu. She confronts Chintu who says he loves her but Raja shoves him off. Raja also discovers his engagement is being called off as Manu is going to marry the new girl in his life! Both Raja and Tanu are enraged and decide to go to Delhi to confront Manu.
But Manu, Kusum and Pappi are in Chandigarh to convince Komal, Payal’s sister-in-law whom Pappi is close to, to run away from her wedding with Pappi instead. Kusum is confused by everyone at the wedding as Tanu, including by Payal, who tells her she’s had a test-tube baby as her husband Jassi couldn’t have kids, but she hasn’t told Jassi the truth. Kusum is getting frantic hearing these secrets and gives Payal a karate chop which knocks her out. Pappi takes Kusum to reason with Komal who’s told Pappi he’s just a friend and she wants to marry her rich Gujarati fiance. Kusum gives Komal a karate chop too and they smuggle the unconscious Komal into a scooter and take her to Jhajjar, where Kusum’s villagers are waiting.
In Kusum’s home, once her family finds out she loves Manu, they attack Manu and Pappi and lock up Kusum. But Omi arrives and saves the day with his logic. The village agrees to Kusum and Manu’s marriage.
Tanu and Raja reach Chandigarh from Delhi and discover Komal has been kidnapped by Manu, Pappi and Kusum. They follow them to Jhajjhar with Jassi, Payal, their baby and Manu’s parents. When they reach, Tanu makes fun of Kusum and says she’s very plain and doesn’t look at all like her – but Kusum snaps at her and says she shouldn’t preen as even her inner-wear is bought by a man while Kusum is a state-level champion who is independent, loving and honest. Kusum snaps at interfering Payal too and tells her to first go and reason with her husband about their baby, which puts suspicious Jassi off the baby right away.
Tanu is startled and Manu makes it clear he loves Kusum.
Tanu is shocked and drunkenly wanders around the village where she tries on a short wig to resemble Kusum. She meets Manu who brutally tells her he doesn’t remember her at all. In the morning, Tanu tells Kusum she’s sorry about her behaviour and would like to stay and help at their wedding.
Everyone sees how Tanu and Manu remain deeply attracted to each other. Payal tries to tell Kusum to forgive them and call it off but Kusum tells her to mind her own business. Raja and Pappi tell Manu to call it off but he doesn’t want to hurt Kusum. Manu tells Kusum he will make a good husband to her and she is satisfied. Meanwhile, Jassi ends up showing his love for his baby again and he and Payal are reunited.
Raja tells Tanu they should leave but Tanu wants to wait. On the wedding evening, Tanu gets drunk and dances in front of Manu in the baraat. Her parents arrive with Chintu and are shocked to see Tanu shattered as Manu leaves for his marriage. Tanu sits quietly in the pandal as Manu is marrying Kusum – until Kusum stops and says she can see how miserable everyone is and she doesn’t want a marriage like this. She confronts Manu, who confesses he still loves Tanu and can’t marry Kusum.
Kusum honourably releases him and walks off, to break down privately.
Tanu and Manu are joyously reunited.
Kusum comes out to find drunken Chintu, delivering an angry speech. She gives him a karate chop.
Tanu and Manu again argue about a tie she had gifted him.
Meanwhile, Raja and Kusum end up having a friendly chat together.