Stones is a finely-balanced, even contradictory play, whose elegant visuals and cultivated language disguise a brutal and dehumanising world. A man and a woman share a prison cell; she at least is free to move, while he stands chained to a pillar. She's a newcomer, we quickly learn, but he's stood like this for years. He's the only survivor of three brothers who one were chained here – able to speak but never to touch, powerless to reach out and offer comfort as, one by one, they died.

It's a nightmarish position to find yourself in, and playwright Katy Matthews doesn't shy away from showing us the horror of the situation or its effect on each of the prisoners. But this is, surprisingly, also a humorous play, with well-judged one-liners and a smattering of physical comedy releasing the tension at just the right times. Perhaps that's why the extreme scenario – which could so easily have felt melodramatically gothic – in fact comes across as alarmingly real.

The whole cast deliver strong performances. Playing newcomer Rose, Emma Howarth is convincing in her descent from optimism to madness; while Chris Gates, as surviving brother Jasper, perfectly captures an image of repressed despair. Trefor Levins and John Black ably carry much of the comedy, appearing in a variety of cameo roles, their characters often conjured by the prisoners' imaginations. And those imaginations aren't entirely healthy ones; we wonder whether the scenes we're witnessing are memories or hallucinations, the product of minds pushed over a precipice by endless incarceration.

Matthews' script tackles some big topics: the strength of family bonds, the isolation wrought by grief, the certainty of faith and what it feels like to lose it. It's a little short on resolution though, and even now I'm not sure I understood the back-story – who was real and who was imaginary, who was sane and who'd gone mad. If Matthews meant it to be ambiguous, then fair play to her, but it might be worth somehow signalling that intent. As it is, I'm left with the nasty suspicion that something in the script passed me by.

But all the same, there's something deeply touching about Stones; about its subtle themes of comradeship, and the characters' quiet determination that no man or woman should be left behind. Extreme situations can reveal profound truths – and amidst all the confusion and delirium, it's the value of human connections that ultimately shines through.