This is partly due to the fact that the Royal Court has an excellent café and it happened to be the press night for the play in the Jerwood Theatre Downstairs which meant that the place was full of hugging actor friends of that cast. The more serious reason is that the play is written entirely in a language invented by Ms Frantzmann and presumably intended to be the childhood invention of the two characters, sisters living in isolation though having to cope at times with a malevolent male world. This is some of the the vocabulary: ‘iccle’, ‘jobbage’ [job], ‘gold star’ [good] ‘an den for afters da main munch, we glugged coffee’, ‘dat she dint thinked it was tiptop to have you round her pup [child]’. If you see it as a means of making an hermetically sealed world of your own and of excluding the adult world from your world (I am afraid the Mitfords’ Hons Cupboard as a comparison came to mind) it works a treat.

One reviewer thought it was some kind of ‘street talk’ but one cannot imagine either sister using this language with anyone in the outside world. No playwright goes to this much bother without a profound purpose. The language emphasises the intense relationship and the strong element of fantasy. The latter is reinforced by the running theme of snatches of songs from ‘The Wizard of Oz’ (which the sister who is less able to read begins in a child’s edition) and the crucial plot device of a pair of red shoes, a version of what Judy Garland wore in the movie (and, like here, was not exactly given them). ‘No Place Like Home’ shoes they are called, echoing the poignant last line of the film. These are two young women who really have never had a proper home. You need to understand ‘The Wizard of Oz’ in the same way that you need to follow the strange language.

There is a single set, a pile of mattresses, packing material and general rubbish. There is no other sign of how anyone manages to live here but it is the dwelling of Pink (Sinead Matthews), the elder sister. Rolly (Ellie Kendrick) arrives straight from her release from prison. Pink is a heroin addict who survives by trading her body for drugs. She takes Rolly in and she intends to keep her entirely to herself. Rolly, heavily pregnant, wants to go straight. She has acquired two connections to the outside world—a friend and a promising job interview, but Pink sabotages both. Pink’s moral compass is non-existent; she manages to justify anything and everything to herself, and she just wants to live with her sister in a drug-induced state.

The performances are astonishing, not least the scenes of being on a heroin high. I have seen Sinead Matthews several times over the years, always playing someone at the extreme end of her emotional tether with self-destruction on the way: Hedwig in The Wild Duck (filial loyalty leading to suicide), Our Class (a villager where the anti-Semitic Poles burn all the local Jews to death), Eigengrau (puts out her own eyes), and the crippled Laura in The Glass Menagerie (arguably in the most brilliant scene with Jim one will ever see). If you want the girl next door, look elsewhere. She picks the part up here by the scruff of its neck and never lets go. I had missed Ellie Kendrick to date. As she stalks the set, wounded, semi-literate and just about coping, you would not guess that her CV starts with Benenden and Cambridge. In the end, Rolly manages to assert herself and to escape, though whether the parting shot of heroin she gives Pink is an act of kindness or an overdose is left unsaid.

The play was commissioned by Clean Break, the excellent theatre company whose education programme helps women offenders and women at risk. PESTS is a very good way to understand the challenge which they face and should be seen for its own sake.

PESTS is a Royal Court Theatre, Clean Break and Royal Exchange Theatre Manchester Co-production.