Kundan Shankar (Dhanush) is the only son of a Tamil Hindu parents settled in Varanasi. Since his childhood, Kundan has had a strong and obsessive one-sided love for Zoya Haider (Sonam Kapoor), a Muslim girl residing in the same neighborhood. He always attempts to be around her but gets slapped several times in the process. Zoya finally changes her mind because of Kundan’s consistency of affection. Her family is orthodox, preventing the lovers from being together. After Zoya moves to Aligarh for further studies, Kundan harmonizes with Zoya’s family, assisting them with chores. Zoya gets into Jawaharlal Nehru University and discovers a long-lost strength as she confronts and then falls for student leader Akram Zaidi (Abhay Deol).
After eight years, Zoya returns to Varanasi, barely recognizing Kundan when she meets him again. Kundan again attempts to ask Zoya for her love but she is reluctant, revealing that she is in love with Akram. She urges Kundan to convince her family about her marriage with Akram. Kundan eventually agrees and gets their wedding arranged, promising Zoya that he will also marry someone else and forget her. He proposes to his childhood friend Bindiya (Swara Bhaskar), who has had a crush on him since childhood.
On the day of Zoya’s marriage, Kundan finds out that Akram is a Sikh, whose actual name is Jasjeet Singh Shergill. This enrages him, as Zoya had used their religious differences to convince him that their match was not possible. He crashes the wedding ceremony and reveals the truth to Zoya’s parents. Kundan is later informed that Zoya tried to commit suicide, and Jasjeet was mercilessly beaten by Zoya’s relatives. At the hospital, Jasjeet tells Kundan that Zoya convinced him to portray himself as Muslim to marry her, a plan he should not have agreed to. While with Jasjeet, Kundan forgets about his own marriage ceremony with Bindiya, taking place that day, and is too late when he returns. Hurt and angry, Kundan’s family disowns him. Jasjeet’s parents take him back to his village. Kundan tries to redeem himself by taking Zoya to Jasjeet’s village. There, he is devastated to find that Jasjeet has succumbed to his injuries, finally understanding that his one-sided love has resulted in an innocent man’s death.