Kathryn O’Reilly’s second play Poisoned Polluted focuses on the fragmenting relationship between two women – in this case, sisters. The play follows the two, known only as Her (Anna Doolan) and Sister (Kathryn O’Reilly), as they’re forced to leave behind the innocence of childhood and face up to an uncertain future that’s scarred by addiction and trauma. As the years pass, their close bond and love for each other becomes twisted into something that will ultimately prove damaging to them both.

As children, the sisters hide out from their mum’s addiction and their dad’s abuse in the local “forest” – which, with the benefit of hindsight, they can now acknowledge was really just a few trees next to the park. That motif of nature as a tainted refuge is present also in Mayou Trikerioti’s set, which consists of printed, peeling sheets that make up a distorted backdrop image of woodland trees.

The play itself is structured as a series of short, sharp scenes which, under Lucy Allan’s direction, often flow seamlessly into one another. These chart the sisters’ downward spiral and the shift in their relationship as Her, who as a child benefited from her older sister’s protection, finds herself suddenly forced to return the favour. Anna Doolan and Kathryn O’Reilly both give excellent performances, meticulously portraying all their characters’ fear, frustration and pent-up resentment, right alongside the love and affection that continues against all odds to hold these two damaged women together. The tragedy of the play is that the two characters need each other – and yet neither of them can truly be happy until they break free of their never-ending cycle of codependency.

While the use of language in the play is important, just as powerful are the moments of silence; movement sequences between scenes (directed by Sophie Shaw), performed without words, evoke the painful emotions that dialogue – even the most poetic – can’t quite capture. Similarly, though they never appear on stage and feature only briefly at the start of the story, the sisters’ parents both loom large as characters throughout, and there are moments when, if we follow the actors’ fearful gazes, we can picture them clearly and feel the anxiety their presence continues to evoke.

As Sister tries again and again to get clean, the play begins to take on a feeling of repetition – but just as we begin to share Her’s frustration and despair, everything comes slamming to a halt with an emotional gut-punch of a final scene. This is a story in which we understand early on there can be no winners, whatever the final outcome, and that knowledge makes it an intense and often difficult watch. Powerfully written and performed, the play shines an uncomfortable light on the ways in which a relationship that should be healthy and innocent can be twisted by the actions of others into something deeply damaging, and how the repercussions of a difficult childhood can continue to be felt even years later.

Poisoned Polluted is at Old Red Lion Theatre until 30th November.