Moon on a Rainbow Shawl is a play of historic importance: Errol John won the Observer New Play award with it in 1957, and in 1958 it was staged at the Royal Court Theatre. For a practically unknown actor and playwright from a distant West Indies isle, this was a signal success; even more notable is that it was written in a creole language. Beneath its passions, torsions, and surface glitter, however, lies a gently conventional plot—one that even this precise, vigorous production cannot quite cover up.

Much of the play's pleasures have to do with the way it plunges us into an unknown, distant culture: lower-class 1950s Trinidad, to be precise. Set in Port of Spain, it opens with an easy Ketch (Trevor Michael Georges) singing and strumming on his guitar. Things darken quickly. Esther (Tahirah Sharif) is a scholarship girl whose parents might not be able to afford the other things (clothes, school materials) she needs to go to high school. Her mother Sophia (Martina Laird) works constantly but struggles with a husband who sometimes fails to come home; he in turn (Charlie, played by Jude Akuwudike) performs menial duties, weighed down by his wasted talent as a cricket-player. At the centre of it all is Ephraim (Okezie Morro), a young trolley-bus driver determined not to end up like Charlie. Moon on a Rainbow Shawl might be called a play about his struggle to leave home, and his home's struggle to keep him there.

If this sounds like it contains the makings of a modern tragedy, that's because it does. Consider for instance Mavis, played ably by Bethan Mary-James. Not quite a prostitute, she nevertheless takes 'Yanks' (short-leave sailors) to bed for a living. Her prideful exchanges with Sophia indicate her hopes for legitimacy; beneath a superbly self-assured exterior, she's a woman on her own. But she lives barely an arm's reach from Esther, and Sophie's attempts to rail against this affront to common decency are met by the landlords's hard-nosed snub: 'If only you could find another who pays as regularly as she does!' Poverty has pushed this community into straits most would rather not think of, and the play's potency lies in taking such unimaginabilities for granted.

Strong acting, especially from Sophia (Martina Laird) and Esther (Tahirah Sharif), keeps us amiably engaged as the play trundles on. It's a shame, then, that Errol John, who (re-)created a remote and vivid world so wonderfully, went on it populate it with characters that are familiar from countless narratives. It's impossible not to recognise the flirtatious, brazen, voluptous woman (Mavis); the old, wealthy, revolting lech (Burt Ceasar as Old Mack); or the pure and hopeful child (Sharif's Esther). Moon on a Rainbow Shawl's weaknesses may be the play's rather than the productions, perhaps, but they are weaknesses nevertheless.

Its programme helpfully includes information on Errol John, on Trinidad and Tobago in the 1940s and 50s, and on Talawa, the company which revives it. Created in 1986 by Yvonne Brewster 'in direct response to the lack of opportunities for and the marginalisation of Black people from cultural processes,' Talawa delivers outreach activities and seeks ultimately to 'enrich British cultural life'. That it has done so is undeniable. But it is difficult to reconcile the play as aesthetic object with the play as cultural instrument. Moon on a Rainbow Shawl is worth staging and worth seeing, but it is not quite "one of the 20th century's great neglected plays".