Beneath London's streets, on the hidden fringes of society, lives a mysterious group known only as the Litterati.  The establishment would call it an underclass; its members call it a family; but to the capital's trend-setters, it's an icon of counter-culture, lauded for being "violent, but not excessive".  Millie, meanwhile, is a well-heeled millennial, who dreams of kick-starting a career in journalism with a feature in VICE magazine.  So when a contact puts her in touch with the elusive Litterati, she jumps at the chance to visit them and immerse herself in their world.

The obvious clash of cultures is a fertile ground for comedy – and sure enough The Litterati is a very funny play, filled with spiky one-liners and deft recurring themes.  But there's more to it than that: Millie's insistent questioning draws out her subjects' stories, gradually revealing their complex and often-troubling pasts.  By the end of it, Millie's learned as much about herself as she has about the Litterati, and playwright Isla van Tricht has made a simple but important point about just how far social mobility extends.

Actor Eleanor Crosswell excels as Millie, a wax-jacketed, wide-eyed young woman who wants to make a difference but doesn't know quite how.  In Crosswell's hands, Millie is likeable enough to care about – yet naïve enough to sustain the humour and keep the dialogue zinging wittily along.  Millie's opposite number among the Litterati, a woman called Dux, is played with equal poise by the impressive Sarel Rose; her bearing and mannerisms embody sassy disdain, yet she's quietly convincing as the protective big sister to a surrogate family of damaged souls.

A stripped-back, industrial set forms a striking backdrop to the action, and the play's themes are well-matched to the Vault's grungy underground vibe.  But I can't help feeling there's something airbrushed about the Litterati: yes, their clothes are dirty, but they don't have a hair out of place.  The darker side of their manifesto is sanitised too, the human cost of their instinct to destroy all too easily forgotten.

On the whole though, it's to van Tricht's credit that she treads lightly, slipping important social commentary into a perky, enjoyable play.  Giving voice to a disadvantaged group is a risky undertaking – it's easy to sound condescending – but the script here is self-aware enough to confront and defuse such concerns.  Director Kate Tiernan hits the right notes too, whole-heartedly embracing the comedy, yet pulling the mood down in an instant when that's what the storyline demands.  With purposeful writing and a talented cast, there's a lot to commend in this softly powerful play.