Balwanth Singh is the bodyguard of Sartaj Rana (Raj Babbar) with high competencies. During one night, Balwanth, along with his pregnant wife, meet with an accident proving fatal for Balwanth while his wife is rescued by Sartaj, and she later gives birth to a child named Lovely. Lovely Singh (Salman Khan), now grown up, works in a security agency. On Sartaj’s order, Lovely busts a human trafficking racket operated by Ranjan Mahatre (Mahesh Manjrekar) and his brothers. Fearing revenge from his enemies, Sartaj calls upon Lovely and appoints him as the Bodyguard of his daughter Divya (Kareena Kapoor).
Lovely Singh is very devoted to his duties but eventually irritates Divya all the time by following her everywhere from her college campus to her classroom. Consequently, Divya and her friend Maya (Hazel Keech) call Lovely from a private mobile number and start a prank love affair, hoping to keep him away from them. Initially hesitant, Lovely gradually starts loving the mystery girl Chhaya but doesn't realise that it is actually Divya calling her as Chhaya. Meanwhile, Lovely protects Divya on many occasions from the attacks of Ranjan Mahatre and his goons. This results in Divya too falling in love with Lovely but is scared to reveal her identity due to Lovely’s immense devotions towards his duties and her father. Further some circumstances lead Sartaj to begin suspecting that Lovely and Divya are in love and they might elope. He sends his men to kill Lovely in case his lover turns out to be Divya. Divya convinces her father that they are not running away and instead Lovely’s love is someone else and is waiting for him at the railway station. Sensing that Lovely might be heartbroken if he does not meet his lover at the station, Divya sends her friend Maya to tell Lovely her true identity. Lovely, after waiting for long at the station platform, finally sees Maya and asks her why she didn't tell him that she is Chhaya. Maya tries to tell him that Divya is Chhaya, but sees one of Sartaj's men in the compartment, waiting for her to answer Lovely. Maya is forced to tell Lovely that she is Chhaya and she loves him As Lovely and Maya hug, Divya calls. In the spur of the moment, Maya throws her phone out of the train, thus erasing Divya out of their love life completely. They both get married but soon Maya dies after giving birth to a child. She writes notes to their son in a diary about the fraud she committed with her best friend Divya and asks him to unite Lovely and Divya.
Several years later, Sartaj invites Lovely and his son to his house, and apologises for his behaviour. Lovely believed that Divya is married and happily settled in London but is shocked to see her there in the house and had still not married,while her look was like married woman. His son grows closer to Divya and even apologises on his mother’s behalf. On their last day of visit, while leaving, he asks Divya to accompany him as his mother. Infuriated Lovely asks his son to apologise to Divya but he refuses and walks away. Sartaj tells Lovely that he too feels the same and requests him to take Divya with him to which Lovely gets obliged to accept. At the railway station, Lovely and his son are accompanied by Divya. His son secretly throws away Maya's diary into trash but is eventually recovered by Lovely. On reading it, he discovers that Divya was his actual lover Chhaya. He calls Divya on her cellphone and addresses her as Chhaya. Divya is overwhelmed with joy and happiness realising that Lovely has come to know of the truth and her identity. She runs toward Lovely and they both hug each other while his son is happily watching them.