I think most of us would agree the idea of building a nest – a place to retire to and shut out the outside world – has been pretty tempting this week. The difference is that Jade and Liam, the couple in Katy Warner’s off-beat love story nest, aren’t sheltering from a temporary weather crisis but from a society in a state of ever-worsening decline, where shopping trolleys being pushed from the roof of their tower block is a daily occurrence, and all the windows have been removed from their stairwell to discourage people from trying to live there.

Jade (Charlotte Jane Higgins) hasn’t left their messy, run-down flat in a long time; she’s comfortable where she is, and sees no reason to risk a trip into the dangerous city streets. We stay there with her, so our knowledge of what’s going on outside mostly comes from Liam (Arthur McBain), who still maintains some social and family relationships beyond their limited circle, and is trying desperately against all odds to find a job. Everything comes to a crisis point when Jade gets pregnant, and the two have to weigh their excitement about being a family against the prospect of bringing a baby into such a messed-up world.

Directed by Yasmeen Arden, the story’s not told in chronological order, so takes a little bit of piecing together – but in a way it doesn’t matter. Jade and Liam’s life together is claustrophobic and repetitive; they have the same conversations over and over, sometimes word for word, and if not for the baby you can’t help feeling that they’d just have stayed this way forever. Their devotion to each other is touching – in a world that’s falling apart, these two vulnerable souls have been left holding tightly to the one thing they know they can rely on – but theirs is also a very dysfunctional relationship, where control and jealousy are a common feature of every conversation.

Arthur McBain’s Liam is the more obviously likeable of the two; wracked by guilt and frustration over what he sees as his own uselessness, he tries to keep Jade happy by bringing her thoughtful gifts and constantly backing down in arguments. But his kind nature leaves him open to manipulation – and not only by her; their first encounter only happens because his friend Pete played a practical joke on him. Meanwhile Jade, played by Charlotte Jane Higgins, is a tougher character to get along with, at least at first. She knows she can get her own way with Liam by sulking and threatening – but it’s only later we begin to understand the intense fear that motivates her behaviour: fear of what’s outside, of being alone, and of what the future holds.

The Vaults’ Cavern space works well as a venue, drawing our eye immediately to the shabby cosiness of Holly Pigott’s set. It’s a total mess, with discarded clothing, furniture and rubbish everywhere and a general sense of not having been cleaned in some time, and yet when compared with its damp, echoey surroundings it does feel like a haven of sorts.

The play, which marks Australian writer Katy Warner’s English debut, was inspired by a true story, and paints an uncomfortable picture of two people left behind by society and looking for a way out. We may not yet quite be at the point of raining shopping trolleys, but that doesn’t mean these characters don’t already exist – and maybe they’re closer than we think.