Two years after Flann O’Brien penned the obituary for his one-time drinking companion, Brendan Behan, O’Brien too was dead.

Behan and O’Brien were two of “a generation of Irish writers who plunged themselves recklessly into the lotus-eating atmosphere of Dublin pubbery,” as Ulick O’Connor put it. Along with Patrick Kavanagh, they effectively drank themselves to death.

But if Behan’s promise was in large part unrealised, the scale of Flann O’Brien’s achievement was only to be truly realised after his death. His audacious, experimental, comic novel, The Third Policeman, rejected during his lifetime, was published posthumously, in 1967.

Subsequent collections of his Cruiskeen Lawn newspaper column, written under the alternative pseudonym Myles na gCopaleen (his real name was Brian O’Nolan), made clear the extent of the loss to Irish letters, and life, posed by his death at 55.

And there was a further literary legacy: an unfinished novel. In Slattery’s Sago Saga, O’Brien concocted the outlandish, satirical story of an eccentric American millionaire, antagonised by the influx of destitute Irish into the US in the wake of the Great Famine, who sought to prevent further famines in Ireland by replacing potato cultivation with a tropical crop called sago.

O’Brien left just seven initial, short chapters of the novel, and Slattery’s Sago Saga would likely have remained little more than a footnote to Flann O’Brien’s canon, had a collection in which it was published not found its way into the hands of theatre director Jo Mangan.

Mangan has a restless, irreverent streak, evidenced in a series of lively productions with her company, The Performance Corporation, that have combined satire with homage in tackling greats such as Voltaire, Tolstoy and Gogol.

A few years after discovering it, Mangan found herself working alongside another Flann O’Brien fan, the actor-writer Arthur Riordan, on a separate project.

Riordan’s 2004 musical, Improbable Frequency, had cast Flann O’Brien as one of the protagonists in a surreal story of Dublin during the Emergency, in the process paying homage to O’Brien’s style as well as his milieu. Mangan invited him to “finish” and adapt Flann O’Brien’s unfinished novel.

The resulting play has just opened in the novel venue of Rathfarnham Castle, Dublin, and runs till Sunday July 25. (See for more info, or book tickets at 01 4627477.)

With so little of O’Brien’s original novel to work from, Riordan’s play is more homage than adaptation. In order to finish O’Brien’s story, he adopted a device used by O’Brien in At Swim Two Birds: at a key point in the play, the characters discover they are characters in an unfinished work, and divide into factions which each try to wrest control of the story.

It sounds, of course, completely barmy – but then so does everything else by Flann O’Brien, as does the previous work by both Arthur Riordan (his debut was a rap musical about Eamon de Valera) and Jo Mangan (try a musical version of War and Peace).

For Mangan, this marks the culmination of a year that initially looked to be catastrophic. Early this year, she got a letter from the Arts Council that told her they liked what she was doing and how she was doing it, but that they were cutting her funding by 35 per cent, on top of a previous cut. From a peak in 2008 of €144,000, funding for The Performance Corporation fell back to €80,000 this year.

The company has responded by diversifying both its sources of income and its products. A Facebook campaign raised €1000; and they hope to raise more from a gala night tomorrow, when the show will be followed by a series of musical acts, including a top-flight mystery guest. (Tickets are €100 and available from 01 627 2827.)

They’ve found the internet to be a source of more than just money: their “theatrical espressos”, or flash mobs, are short theatrical events that erupt spontaneously in the middle of the city, catching passers-by unawares, with the event recorded for viral distribution online.

February last saw Mangan directing one such event in Washington DC, as part of an ongoing collaboration with the Irish-American arts centre, Solas Nua: to the surprise of morning commuters, a plaza in central DC suddenly became the scene for an epic hurling match, fought with snowballs instead of sliotars.

In another theatrical espresso, the company marked St Patrick’s Day in Dublin with a sudden mass ceilidh outside Central Bank. (Search YouTube for “Performance Corporation” to find these and others.)

Flann O’Brien may have mocked those who traded on the Irish language and traditional culture as a badge of self-righteous identity, but he also knew the loneliness of being unappreciated as an artist, and struggled all his life to find an audience worthy of his work.

Mangan briefly felt that loneliness this year, as she faced the realistic prospect that her company might not survive the cuts. (Further cuts would jeopardise its continued existence, she says.) The theatrical espressos show a determination to find new audiences and new sources of income in difficult times, and a willingness to use both new media and traditional culture to do so.

That’s the kind of tenacity that has allowed them to bring an unfinished novel by an Irish master to the stage. This should be a saga worth following.