A couple, weary and half-asleep with their twin babies in tow, tragically meets with a fatal car accident, leaving the twins as the sole survivors. Their uncle, Kartar Singh (Anil Kapoor), who relishes his life as a bachelor, makes the difficult decision to separate the twins. One baby is sent to live with his sister Jeeto (Ratna Pathak) in London, while the other is entrusted to his brother Baldev Singh (Pavan Malhotra) in Punjab. Time passes, and the twins grow up in starkly different environments: Karan (Arjun Kapoor) thrives in the bustling lifestyle of London with his aunt, while Charan (Arjun Kapoor) leads a humble life in Punjab, managing a car showroom.
Karan, enjoying his freedom and absence of commitment, has been dating Sweety (Ileana D'Cruz) for two years. However, complications arise when Jeeto and Sweety cross paths at a mall; misunderstanding and accusations flare up between them, resulting in an emotional quarrel where Jeeto labels Sweety a "bad girl." Meanwhile, in Punjab, Charan finds himself in a predicament of his own as he is in love with Nafisa (Neha Sharma), a law student and a Muslim, but his father Baldev insists on an arranged marriage with a Punjabi girl. Jeeto has her sights set on a match for Karan with Binkle (Athiya Shetty), the daughter of family friend Akalpreet Sandhu.
Karan learns of Jeeto’s marital wishes for him while in Punjab and cleverly convinces Baldev to propose Charan for Binkle instead. The plan succeeds, leading Baldev to take Charan to London to meet with Kartar, who welcomes them with open arms. Throughout this time, Karan's life intertwines with Sweety’s, and Charan finds himself battling a sudden infatuation for Binkle, despite his determination to avoid marriage with her.
Kartar, with his deft problem-solving skills, proposes Charan should pretend to be a substance abuser to deter Binkle's family from considering the alliance. Amusingly, when Charan's supposed addiction backfires, leading to chaos, jealousy, and misunderstandings, he ironically finds himself truly enchanted by Binkle's sweetness.
As the weddings draw near, familial pressures mount, and secrets unravel, causing emotional turmoil. Charan's struggles culminate in a heartfelt moment where he finally declares his love for Binkle, but misunderstandings continue to plague both brothers. With the tension escalating, Kartar dreams of the twins’ late father urging him to rectify the chaos he inadvertently helped create.
On the fateful date of December 25th, in a twist of fate, Karan and Charan decide to swap their identities just as their respective weddings commence. Amid the chaos, Sweety publicly confesses her love for Karan, bringing shocking revelations to light. In a confidential discussion, both brothers reveal their switched identities to Kartar, who decrees that the only way forward is for them to embrace their true selves. Thus, Karan ends up marrying Sweety, while Charan ties the knot with Binkle, amidst the laughter and tears of family gatherings.
