There are some moments from Tamasha’s production of A Fine Balance, which has premiered at the Hampstead Theatre, that I will remember for long time. There’s the opening scene, of a legless beggar, who skims around the stage seeking alms amid an imaginary traffic jam, evoked by a soundscape and smellscape that immediately transported me to Calcutta, the site of my first encounter-shock with the sub-continent. Then there’s the stunningly effective puppetry that solves the problem of animal and child characters – the “death” of one animal puppet produces an almost audience-wide audible gasp.

Yet these excellent moments are blended to produce a dull, if worthy, whole. The play is based on the eponymous Booker-shortlisted novel by Rohinton Mistry, one of those classic Indian sprawling epics, in this case exploring the impact of Indira Gandhi’s 1975 Emergency, which imposed martial rule on the world’s “largest democracy”.

The story, by and large, is of the effects on the poor – the slum-dwellers thrown out of their homes and driven into pointless stone-breaking, morale-sapping labour; their employers, only marginally more economically secure, left without workers; the men and women sterilised by force … the novel is a great sweeping tale. The play takes in all of their stories, yet while it leaps from drama to drama, from crisis to crisis, the action on stage is slow, even langorous. This is a neat synopsis of a play, but the heart, the soul, is missing.

Part of the problem is that none of the characters is developed – they are more archetypes than people. I naturally sympathise with Dina Dalal (Sudha Bhuchar). We meet her as a sweat-shop employer, but she gradually emerges as a struggling woman, a widow, determined to maintain her independence in a male-dominated world, if only to remain out of the uncaring clutches of her bullying brother. But she is a stereotype, if an admirable stereotype; we never learn more. What was her relationship with her husband; what gave her the steel to battle on to the bitter end? (The book answers these questions; the drama does not.)

It is her developing relationship with two tailors – Rehan Sheikh’s Ishvar and Amit Sharma’s Omprakash – that is at the centre of the play, but again these characters – the outcasts who flee to the city after their family is victimised for its courage by higher-caste oppressors – are pure stereotype. They suffer a dreadful fate, but while it is easy to see them as symbols of caste oppression, it is hard to feel much for them as victims.

The cast is not really at fault here – they do a good-enough job with the material at hand, with Divian Ladwa as the innocent, country-lad-in-the-city Maneck (who boards with Dina) particularly strong, but there’s little for them to really work with.

Another problem arises from their number. Many minor characters pop on and off the multi-level stage – played in rotation by the cast of eight – yet these are inadequately differentiated by costume, gesture or style. Oh, you think, Mrs Gupta (Sameena Zehra), the pushy, uncaring purchaser of Dina’s efforts, is also her brother’s well-meaning but helpless wife. She’s not Ruby, but the Mrs Gupta-actress playing Ruby.

I wouldn’t say don’t go to see this play – it is an entertaining-enough evening, but to produce a gripping, momentous account of this key moment in Indian history required more: more actors, more passion, more narrative, more pace.

The production continues until January 29. Links: the the theatre (with online booking), Tamasha. Other views: the Guardian’s, The Times’s and the Telegraph’s.