It’s abrupt. It’s violent in word and, to a certain extent, in deed. It’s also very good. Vivienne Franzmann has been a teacher, so her portraits of teenagers and adults trapped in concentric circles of desperation as a playground bullying incident escalates into full-blown tragedy ring true. This is Franzmann’s first full-length play, and it’s already won awards; it will be fascinating to see what she writes next.

Mogadishu is well-served by designer Tom Scotts minimalist setting of a revolving metal cage within which chairs, a table or a breakfast-bar are imported to present new the different locations within which the three main characters play out their non-school lives. These are teacher Amanda (Jackie Clune), her troubled teenage daughter Becky (Rosie Wyatt) and playground gang-leader Jason (Ryan Calais Cameron).

Becky self-harms, partly because of her father’s suicide. Jason’s mother had also killed herself, which is why Amanda is unwilling to press for Jason’s exclusion from school after he knocks her to the ground as she intervenes in his attack on fellow-pupil Firat (Michael Karim). Then Jason coerces his “gang” – including girl-friend Dee (Savannah Gordon-Liburd) – into backing his own (fictional) version of events.

Director Matthew Dunster coaxes some excellent performances from his predominantly young cast, especially from Wyatt, Gordon-Liburd, Cameron – who gives us the pain as well as the malevolence of Jason – and Karim. Clune is also very fine, notably in her encounters with school head Chris (Barriscale) and laid-back second husband Peter (Jason Barnett) as well as in her relationship with Becky. There’s an authoritarian stature to Nicholas Beveney as Jason’s father Ben.

Vocally, it all goes at a cracking pace, so that some of the street-slang slipped past me – though the younger members of the audience in Cambridge picked up on it with delight, so it obviously rings true to their ears. That’s an achievement in itself, for it’s something which is very difficult to realise. These people are real human-beings, not mere stereotypes. You may not like them. You may think what they say and how they behave is wrong. But you do believe in them.