Rajiv Malhotra (Sachin Khedekar) is returning to his home to be with his pregnant wife Ankita. On flight he befriends Charles unaware that he is a smuggler. Charles uses Rajiv to smuggle diamonds into Mumbai, when he is going to meet his preggers wife in Hospital. Ankita gives birth to twin boys and Charles comes to congratulate him at their house. But Rajiv comes to know about him and calls the police in the mishap Charles runs away with one one of the twin. Police arrest him but he claims the kid died in a blast. Rajiv Malhotra shifts to London with Ankita and his son Prem (Varun Dhawan) for safety reasons, where as the other twin is alive and grows up in the slum of Mumbai by the name of Raja (Varun Dhawan). At birth the twins were joint at the arms and were separated, so they share reflexes and Raja was the strong one and Prem weak. The doctor also predicted as one becomes weak, the other will become stronger.Prem is in college now and is being bullied. Samaira (Taapsee Pannu) is his only friend. Raja beats up a mafia's son Alex (Vivan Bhatena) at a Bappa ceremony and is advised to leave the country. He enlists help of Pappu Passport (Johnny Lever) to escape to London. Raja meets Alishka Bakshi (Jacqueline Fernandez) on the plane and falls in love with her. Officer Dhillon (Pavan Malhotra) is after Raja as he is an illegal immigrant in UK. Meanwhile Prem and Samaira are friends but Samaira's mom (Upasana Singh) is after her to ensnare Prem in her love. Raja kisses Alishka, and by reflex Prem kisses Samaira. Now Prem's dad Rajiv takes him meet his childhood friend Balraj (Anupam Kher) to meet his daughter who is Alishka. Alishka is all over Prem, but Prem runs away from her. Officer Dhillon mistakes Prem for Raja and is now after him. Samaira runs into Raja (thinking he is Prem), who defends her from goons and ends up winning her heart. Again, in a case of mistaken identity, Raja fights the bullies of Prem's college and ends up again impressing the heck out of Samaira.Now Rajiv gets a call from Charles who is about to be released from jail. Charles vows to destroy Rajiv and his family. Rajiv has an accident and is rescued by Raja. in the hospital, Raja runs into Alex, whom he had beaten in Mumbai. Turns out he is Charles's son and has lost his memory.Prem selects a ring for Samaira, but then Raja's friends Nandu & Sharafat Bhai come into the store and Prem (of course) refuses to recognize them. They are hurt. Prem and Samaira leave and then Raja & Alishka come into the jewelry store. The store owner mistakes Raja for Prem and gives Samaira's ring to Alishka, who is ecstatic. Balraj calls Rajiv to congratulate him on Prem and Alishka's engagement. But Prem refuses giving the ring to Alishka. Samaira hears the conversation and breaks up with Prem. Now, finally, Prem and Raja run into each other and figure out the confusion. Raja asks Prem to meet Alishka as Raja, and to get her back. while Prem asks Raja to meet Samaira as Prem to win her back. In the confusion, finally the girls figure out that Raja and Prem are twins.Now Alex gets his memory back & reunites with his dad Charles. Alex kidnaps Raja's friend Nandu and forces Raja to bring Prem and Rajiv to him. Raja does his bidding and Alex locks him up so that Raja cant fight and starts beating Prem. Raja starts Kung Fu fighting in the cage and Prem has reflex actions by which he beats Alex. Raja and Prem then save Rajiv and then get married to their girls.