Tomorrow night, TAG Theatre Company ends its Citizens’ run of Yellow Moon and prepares for a three-week tour of schools and colleges - a total of 28 performances that will take them from Invergordon to Dalbeattie, with time for a stop-over at Islay High. For their playwright, they have turned again to David Greig, whose Petra and Dr Korczak’s Example have been such successes for them in the last decade.

This time he has written a tough fantasy about Leila and Lee, two troubled adolescents from Inverkeithing who find a kind of purgatorial redemption in the Highlands. It is in the style of an audio book, with the action described, and the unspoken - maybe even unarticulated - thoughts of the characters spelt out for us. While it is the kind of theatre you could absorb with your eyes closed, the electric performances of the cast of four banish the very thought. Designed as it is for widely-scattered school halls in broad daylight, it is a stage manager’s dream, with no props or scenery, and minimal furniture and dressing up.

Instead, everything depends on Greig’s vivid, taut writing, by turns harsh, humorous and poetic, played for all it’s worth by the quartet of actors, with the audience hanging, sometimes with bare knuckles, on every word.

Because the play has (to quote the programme) “swearing and some challenging content”, TAG recommends it for audiences aged 15 and over. I saw it in the Circle Studio at the Citizens Theatre in Glasgow (where TAG is now the co-resident company) with one of the 15 schools that booked there. The fourth years were fiercely attentive, though predictably the rough (and later tender) wooing and swearing provoked a little nervous laughter.

But for all the social “realism” of the piece, the story is the kind of which ballads, old and new, are made. To underline the point, Greig subtitles the play The Ballad of Leila and Lee, and the fictional alienation is reinforced by Leila’s insistence that she thinks of herself as a character in someone else’s story. And, as in the way of ballads, the family situations and personal interactions will be meat and drink to the school counselling services.

Leila’s adolescence is made bearable by self-harm and celebrity magazines.

Lee is from a single-parent family, or would be if his mother stopped treating her depression with alcohol, his father having left home suddenly after knifing someone to death. His only ambition is to be the first pimp in Inverkeithing, a career he offers to share in some part with Leila.

Lee is attached, for the best of reasons, to his baseball cap and, like father like son, fatally stabs his mother’s new partner in a quarrel over the headgear. Desperate for help, Lee decides to look for his long-lost father somewhere near Inverness. “Are you coming or are you coming?” is an offer Leila cannot refuse and, with stolen money, together they make a ticketless rail journey to the north where, in the way of ballads, the wildness of the Highlands and the people they meet there conspire to heal their urban hurt.

Unusually for TAG, and because of its sensitive content, the production is not seen particularly as an opportunity for classroom work. Instead, TAG’s acting education officer Angela Campbell is offering workshops to all who want them, and for many there will be after-play discussions.

Also, the TAG website is publishing selections from the diaries that director Guy Hollands has persuaded the cast to write. These frank and personal comments, much in the way of the no-frills production, go a very long way in laying bare the art of theatre.

TAG, tel 0141 429 5561www.tag-theatre.co.uk