Danish (Dhanush), a mute whose childhood dream was to become a Bollywood actor, reaches Mumbai to fulfill his dream. He tries to enter the film city there, but gets stopped by the guards there. He trespasses the gate and comes across an Assistant Director, Akshara Pandey (Akshara Haasan), who is amazed by his acting. She approaches a director for requesting a role for Danish in a film, but the director refuses after he comes to know that Danish can't speak.
Danish and Akshara go to a voice hospital to get his check-up, but doctors declare his vocal chords are fully paralyzed and are unable to be treated. But, they assure him that with their advanced technology, Danish could have a 'voice transfer'. They fit a chip inside Danish's larynx with which a person could transfer their voice into the chip, and when the person would speak, the words will also come from Danish's mouth. They set out to search for a person who could speak for Danish every time, when they come across an old drunkard, Amitabh Sinha (Amitabh Bachchan), lying on the footpath. Amitabh also wanted to become an actor but was rejected because of his voice.
Danish approaches the director again, who agrees to launch him this time, but wanted him to change his name. Danish searches for a name and concludes on Shamitabh (the combination of DaniSH and AMITABH), giving credit to the person who provided him with voice. Shamitabh makes a couple of movies and turns out to be a hit actor to which Amitabh realizes was only because of him and an ego problem between the two starts to rise. They both separate and start making their own movies, where Shamitabh plays the role of a dumb person and Amitabh dubbing the voice for another actor. Both movies end in a flop at the Box Office.
Akshara makes both of them realize they are nothing without each other and gets them together for yet another film, titled 'Sorry' which is directed by Akshara herself. Meanwhile, Akshara and Shamitabh tell that they like each other.
Amitabh and Shamitabh were happy about the success of their movie, but faced a fatal accident due to which Danish loses his life, and Amitabh's larynx damages completely making him unable to speak.