The Lost O’Casey at Dublin Theatre Festival. Photo: Patrick Redmond

“Imagine not being able to remember,” says someone with tearful eyes, early in The Lost O’Casey. It’s really a heart-rending moment; this man, as passionately informed as a historian, is losing his knowledge of Dublin’s history.

There’s more than one reason to mourn memory loss in this excellent piece of immersive theatre, co-produced by ANU and the Abbey Theatre, which reimagines a forgotten Seán O’Casey play from 1924. After all this time, the characters of Nannie’s Night Out, a tragicomedy about homelessness and addiction, fit seamlessly into the present. How much can we say has changed?

When we meet a weathered guide on the street (Michael Glenn Murphy), comparing the lifestyles of pigeons and hipsters, his witty observations of contemporary life chime with the street philosophy heard in O’Casey’s plays. But he also draws attention to current issues, such as a social housing complex being demolished for a new cultural district.

Director Louise Lowe is on fine form here. More than once, her thrilling promenade production focuses our attention like a close-up in a film, allowing performers to come abruptly into view. Nannie (Sarah Morris), for instance, will arrive bloodied and disorientated, taking us to a medical van where a subtle dialogue between patient and doctor (Leanna Cuttle) reveals bureaucratic red tape and class differences, while stealthily exposing our own prejudices. (“I don’t know who attacked her,” I tell the doctor, already forgetting it was the police).

For its breakneck pace, the production still finds time to be still and compassionate. In a condemned building, Morris’s Nannie speaks of her abuse with the gentle appeal of someone wanting to be heard. Nearby, a championship boxer, in Robbie O’Connor’s superb performance, unravels with self-loathing. It’s as if Dublin’s inhabitants, much like the city’s vanishing social housing, are on the brink of destruction.

Along the way, we’ll hear clarifying affirmations and surreal omens. “Death isn’t the worst thing,” says Nannie, “I think being forgotten is the worst thing.” That opens up devastating cycles of people lost through neglect and blame.

If you end up at a drug-fuelled party, murky like a nightmare in Owen Boss’s painstaking design, chances are you’ll feel for the men whose past glories flash before their eyes. The production quite sombrely shows us the door, knowing the city will soon move them on somewhere else, as if whispering: never forget.

The Lost O’Casey is on as part of Dublin Theatre Festival until October 13. Click here for more information.