Roy WilliamsCategory B opens the Tricycle’s Not Black and White season, in which a trio of plays examining the experience of black Londoners in the 21st century will be running in repertoire until December. And, if this first night is anything to go by, audiences at the Kilburn venue have an extraordinary few months ahead of them.

Category B prisons, we are told by prison guard Angela, are the sorting office for the penal system, the point of arrival for all prisoners and the place many will pass their sentences. In theory, the murderers and rapists are transferred on to more secure units and petty criminals moved to lower grade prisons. But in reality the system suffers such overcrowding that ‘cat Bs’ count amongst their inmates criminals from across the spectrum.

Williams acknowledges in a programme note that he is embarrassed and angered by the racial demographic in prisons in this country, but the playwright is firm in his conviction to make power, not race, the subject of his drama. Category B looks at the complex relationships between inmates and guards and within each of those groups, providing a sense of the delicate political manoeuvring necessary to keep things running smoothly.

Angela (Sharon Duncan-Brewster) has been in charge of her wing for long enough to know which rules must be adhered to and which may be broken. She appears to take great pride in her job but reacts with cynicism to new arrival David’s (Kobna Holdbrook-Smith) desire to make a difference. This contradiction provides a fizzing undercurrent to the play, keeping us guessing about Angela’s motivation. Duncan-Brewster inhabits Williams’ writing entirely, revealing a character who can confound us with her actions yet draw on our sympathy. The relationship with senior officer Andy (Robert Whitelock) is particularly engaging, Whitelock’s quiet and considered performance providing an effective contrast to Duncan-Brewster’s more spirited one.

Angela may hold the keys to the wing, but the person actually running things on the ground is Saul (Jimmy Akingbola), serving time for an unspecified crime. His interactions with sidekick Riz (Abhin Galeya) are illustrative of the boredom engendered by the system. It is at moments like this that Williams’ subtlety shines: as Riz gabbles endlessly to a silent Saul about his favourite Eighties films, kung-fu kicking his way around the stage, we get a clear sense of what daily life inside must be like; Williams has no need for didacticism to make his point. Paulette Randall also merits praise for her evenhanded direction, particularly evident at this point.

Saul, as part of a tacit agreement with Angela, directs the wing’s narcotics trade. One of his customers is fellow inmate Errol (Karl Collins), a man with a dangerous reputation and a quick temper. Shortly to be granted parole, his life is unbalanced by the arrival on the wing of Rio, a young man he knew as an infant in the days before his incarceration.

Collins’ performance is an extraordinary one: Errol’s feelings of resentment and humiliation at his situation seethe beneath the surface; Collins captures perfectly the emotional instability of his character, by turn revealing Errol’s intelligence and tenderness and shocking the audience with his explosive displays of frustration. Williams does not ask us to sympathise with Errol – the man is too selfish for that – but he does ask us to consider what happens when a human life is deprived of its dignity.

Rosa Maggiora's set provides a understated yet effective physical context for the drama laid before us, with James Farncombe's lighting design conjuring up an atmosphere which feels at times as stark and uncomfortable as an interrogation room, and yet as gloomy as the grave.

Category B sets out to examine power relationships within the British prison system, but such is the richness of Williams’ writing that the play touches upon many more issues than just this. The paucity of male role models in black families, the consequences of betrayal, both romantic and professional, institutionalisation in the prison sector, and the anti-Muslim sentiment inherent in the system; all of these come to the fore, each explored with an unrelenting curiosity.