And yet, for all the intelligence that characterises Shamitabh, what the film lacks is heart.

Somewhere near the middle of R Balki's new film, the hero Shamitabh (Dhanush) attends a film awards ceremony. When he wins Best Actor, he goes on stage and the award is presented to him by Rekha, playing herself. The applause is rousing, Shamitabh is clearly overwhelmed. He takes the microphone and after a beat of silence says, "Thank you" in that rich, distinctive baritone that is unmistakably Amitabh Bachchan's.

Rekha catches her breath, her red lips part, her eyes widen and she stares at the man before her as though seeing him for the first time. She leans over to him and says throatily, "I'm so proud of you. ... You are truly God's gift," she pauses, "to cinema." Clearly, we can add Rekha's name to the list of Bollywood actors who can make fun of themselves and their past. The moment she hears Shamitabh speak, adoration fills her face and you can easily imagine that her pulse is beating faster, that her heart is pitter-pattering and she's replaying "Neela Aasman So Gaya" in her head.

This scene with Rekha is one of many little Bollywood tributes that fill Shamitabh, R Balki's new film about those who work backstage and help turn an actor into a star. The film begins with a premiere and the last shot before end credits is of a movie script — Shamitabh is all what makes Bollywood so charming. Here, dreams — punctured as they may be by ego, bitterness and insecurity — do come true, even if it is fleetingly.

Dhanush plays Daanish, a young man who is born mute but is obsessed with cinema and determined to be a star. Everything he learns in life is from the films he watches, picking up tips on how to woo a woman from Cary Grant and telling his school teacher that Mahatma Gandhi's wife was Rohini Hattangadi. Like Rajinikanth (Dhanush's real-life father-in-law), Daanish works briefly as a bus conductor before heading to Mumbai, with hopes of acting in a film by either Raju Hirani, Rohit Shetty or Karan Johar.

Of course, that doesn't happen. As if it wasn't bad enough that he's a nobody, Daanish is, after all, not just metaphorically voiceless, but literally so. A young assistant director, Akshara (Akshara Haasan) takes pity on him and then realises he's a powerful actor. But what good is an actor if he can't speak?

Enter Amitabh Sinha (Bachchan), a grizzly alcoholic who lives in a cemetery, likes to be called "Jahapanah" and has a baritone that sounds like thunder, velvet, dark chocolate and single malt whisky are having a non-stop (and occasionally violent) orgy. Decades ago, he came to Mumbai with dreams of becoming a star, but was rejected by films as well as radio, as Bachchan had been in reality. However, while Amitabh Bachchan went on to climb the heights of stardom, Amitabh Sinha plunged the depths of alcoholism. When Akshara and Daanish come to him, asking him to give the mute actor his voice, it's a chance to bring his old dreams to life.

The relationship between Daanish and Amitabh is fascinating and volatile. This is no candy-flavoured friendship in which one is happy to be in the background. Amitabh is convinced that his voice is what makes Shamitabh a superstar and Daanish is determined to prove that without his physical charisma, the voice would be irrelevant. Mediating between them is Akshara, a kind, ambitious and no-nonsense assistant director who hopes to cast Shamitabh in her first film.

The performances in Shamitabh are all powerful. It's young Haasan's debut film but she holds her own against two superstar actors. Dhanush doesn't have a single word to say in the film, but that doesn't stop him from communicating everything from Daanish's frustration with his disability to his shy crushing on Akshara. The film-within-a-film scenes show nothing of Daanish's acting talent — which is why you find yourself siding with Amitabh who credits Shamitabh's charism to his voice — but Dhanush as the silent Daanish shows how much an actor can communicate without words. Bachchan's voice resounds gloriously in Shamitabh, whether he's drunkenly talking to a tree or reciting dialogues from Mughal-e-Azam. It's been a while since Bachchan was in a film that utilises both the actor's flair for drama as well his comic timing, and Bachchan in Shamitabh shows he can still make the crowd break out in appreciative whistles and applause.

The weakest link in Shamitabh is the brief interlude of science fiction, in which transmitters and speakers are surgically inserted into Daanish. Now, anyone in possession of the headset that matches with those transmitters and speaker, can be Daanish's voice. They speak, the transmitter in his throat picks it up, sends the signal to a speaker (also in his throat) and after a short time lag, Daanish is "speaking", much like a ventriloquist's dummy. Bollywood has come up with a lot of outlandish "logic" in its time, but even by the standards of an industry that would have us believe snakes lap up breast milk and a knock on the head can cause/cure everything from amnesia to blindness, the "science" behind Shamitabh is a whole new level of bunkum.

Balki's hope as a writer and director is that the central idea of two egos wrestling for the upper hand within one persona will make us ignore the unconvincing technology behind Shamitabh, a composite of Amitabh's voice and Daanish's body. To some extent, Balki is successful.

Shamitabh is a funny, clever film that is entirely aware of how funny and clever it is, and how that makes it better than most dreary Bollywood releases. Fittingly for a director with roots in advertising, the product placement in Shamitabh is some of the best seen so far. It ranges from cheeky — a film called Lifebuoy in which the hero, named after the soap, is committed to protect the country's tandurusti — to subtle, like the plugs for Amazon that are scattered all over the film. Balki also comes up with some little details, like Daanish's "five star accomodation" when he first comes to Mumbai, which are delightful.

And yet, for all the intelligence that characterises Shamitabh, what the film lacks is heart. Perhaps it's the effort of balancing the gentle parody of Bollywood with the sensitive drama of Daanish and Amitabh's struggle for power, but Shamitabh isn't as moving as you'd expect a Balki film to be. We spend two and a half hours with Daanish and Amitabh, but when we come out of the theatre, it doesn't feel like we know them. All Daanish is his disability while Amitabh is his whisky-laced ego. Much like Balki's previous films, Cheeni Kum and Paa, Shamitabh has a wonderful premise and a good buildup, but flounders as it nears the climax. The end is drearily predictable, particularly since it seems Balki has a pattern for how his films must end.

Still, despite the flawed writing, Dhanush and Bachchan make Shamitabh a pleasant enough outing to the movies.