It’s a “messed-up tradition” says one of the characters in Charlene James’s play. Female genital mutilation, an illegal practice in Britain, is performed in backrooms on girls who are led there by mothers, aunts and elders. A gripping piece of urban noir, Cuttin’ It combines a strong social message with bursts of humour and a slow-dial suspense that crescendos into a gritty tower-block tragedy.

James’s script follows the chalk-and-cheese friendship between two British Somali schoolgirls who meet on the number 47 bus. James won awards for this play in 2016 and it has lost none of its terrible power under the direction of Nickie Miles-Wildin.

Asha Hassan plays Muna, a streetwise 15-year-old who is trying to protect her six-year-old sister from FGM. Hermon Berhane is Iqra, a recent immigrant with a backstory of war trauma: all her family were killed in conflict and she sits on the bus, still numb with shock, trying to remember their names.

The drama is delivered mostly through parallel monologues on Amanda Mascarenhas’s spare, industrial stage, which is part concrete staircase, part steel scaffolding.

Their stories encompass first friendship and then betrayal. Muna speaks in an endlessly entertaining stream of quick wit and worldly backchat, while Iqra is quieter and seemingly more naive. Berhane uses British Sign Language alongside spoken word, bringing a visual poetry to some scenes. Under a spotlight, Iqra’s hands flutter to a Rihanna song on her iPod or to a childhood memory.

Muna is a better realised character than Iqra and Hassan is a charismatic, confident performer, bringing out the humour and heart in her lines. The actors’ delivery does not always stay even, but James’s script is such a tour de force of vigorous, impactful writing that it carries us along.

Only on a few occasions does the play’s social message sound over-emphatic or bolted on. On the whole, the arguments against FGM are developed within plot and character and carry much of the suspense. The terrible twist at the end can be seen coming, but this does not lessen the tension of a great, gripping drama.

• Cuttin’ It is at the Royal Exchange theatre, Manchester, until 1 February.