Octagon (Arcola)

Welcome to the world of American performance poetry, and a verbal cornucopia that has 'message' writ large in every line and where protest is a whisker away from personal pain and tragedy. Writer Kristiana Rae Colón describes herself as "a poet, playwright, actor and educator" and all four facets are highly visible in this wrangling, gut-wrenching exploration of the competitive spirit. She doesn't actually appear herself as a performer, but her sense of showmanship imbues every scene.

In Octagon, a national poetry slam is the framework and we see the build-up, the battle to find the final member of the team, and the tangle of relationships between seven participants and the oddly-named Watcher Named Pen, who ironically describes herself as "the bar bitch with access to a mic… the show host with tits".

One of the poets, Prism, also happens to like rough sex, especially involving erotic asphyxiation, and she practises this with both her current lover, Tide, and the victorious newcomer to the slam team, Atticus, a man "from nowhere". The play therefore explores themes of self-destruction alongside salvation. For all the personal issues of the contenders and their reasons for seeking the gratifications of celebrity, it exerts its dramatic grip only slowly.

There is no doubting the skill of the performers, all perfectly cast, and the dexterity of director Nadia Latif, who weaves a kind of magic out of the relentless barrage of words, but after two and three-quarter hours one is left beaten into submission, and wishing that the writer had taken her own advice in the character of Chimney, a "winner", who urges Palace, a "dreamer", to trim his poem to a more suitable length.

The main difficulty is that the poetry, supposedly from seven different voices, not only begins to adopt the same tone, the same rhythm, the same abrasive, quickfire rap-like delivery whoever is speaking, but that when the characters are simply having a conversation, their language is similarly heightened, as if they can't help but speak in striking images and semi-rhymes. This gives the play a self-conscious quality that may have been intended – indeed it is in many ways as much about self-consciousness as self-expression – but it lowers the dramatic temperature.

That said, the cast have precision, energy, conviction and huge aplomb. Lara Rossi, Solomon Israel, Asan N'Jie, Leemore Marrett Jr, Martins Imhangbe, Harry Jardine, Crystal Condie and Estella Daniels create a blistering ensemble, but there is an earnestness about the whole evening that bogs it down just when it should be moving forward.

At one point, Palace says "I want to write happy poems. Is that a thing? Joy poems? Do poets get to be happy?" One wished for a little more lightness of touch such as this.

Octagon runs at the Arcola until 17 October