In 1904, in a small, ragged parlour in a house in the Hill District in Pittsburgh, Pennsylvania, nearly 40 years after the official abolition of slavery in America, a mismatched group of black people are struggling to find a way to survive and thrive in a white world.

Solly Two Kings (Joseph Marvell), professional dog-shit collector, looks like a buffoon, until he explains that his stick is notched 62 times, for each slave he helped guide to freedom on the Underground Railroad. He sums up the predicament these ex-slaves and younger freeborn Blacks face: “Freedom. I got it, but what is it? I still aint found out.”

Eli (Lucian Msamati), his friend and comrade, is building a wall around this house, hoping to keep its inhabitants safe, with the help of an intruder, the ironically named Citizen Barlow (Kobna Holdbrook-Smith), who looks like a man with problems. He’s tried to find a decent, fair-paying job, and failed, but the weight on his shoulders is more than that.

Always in the house is Aunt Esther Tyler (Carmen Munroe), who claims to be 285 years old, and certainly is regarded, almost worshipped, as a seer and problem-solver. She’s also fervently religious – but does this really help the people she guides? Caring for her is Black Mary (Jenny Jules – who is notable for a really stunning stage presence), who has fled the “Uncle Tom” ways of her bullying brother Caesar (Patrick Robinson), who has chosen to carve out a place for himself by enforcing the white men’s law.

The play is Gem of the Ocean, the work of August Wilson, who died last year at the tragically young age of 60, and one of a cycle of ten that, decade by decade, tell the story of the black experience in America. It is the fifth of his plays to have UK premieres at the Tricycle Theatre in Kilburn, that northwest London theatre jewel.

They are wonderful characters, in a setting that feels both well-researched and emotionally real. But the weakness is in the pace of the story-telling. The play is slow and meditative, we go around, and around and around the same points about the local mill, the treatment of its workers, and the almost hopeless position of the men and women trying to find a way to real freedom.

The subject is so worthy, and the high points so worthwhile, that it is even more frustrating that in between there are long minutes in which you wish the playwright and director (Paulette Randall) would just get on with it. Two hours and 45 minutes is a long time to be held in the theatre by just seven characters.

This is, however, one of those plays everyone should see as part of their cultural and social education. Just go prepared with a good pill of patience.

A special word of praise must go to Libby Watson’s set. Aunt Esther’s parlour is lovingly created with great realism, except that the floor is dipped into a U-shape. The raw boards make a hugely effective ship as Rutherford sails off to the metaphorical “City of Bones” to relive the whole of Black experience in Africa and America. It also emphasises the tenuous footing of all the characters – the fact that a hideous, violent fall is only a step away.

Links: The theatre, with online booking; other views – Independent, the Observer and The Times.