The notice pinned up outside the Arts Theatre warns: "Eden contains language that some patrons may find offensive." It might as well read: "Eden contains language that some patrons may find incomprehensible". This Irish two-hander - a series of linked monologues in which a couple recount the events of a pivotal evening in their decade-long marriage of disappointment - is so full of Derry colloquialisms delivered in such thick accents that it initially makes the head spin.

In fact, when Don Wycherley, playing husband Billy, first opens his mouth to speak, there are gasps of astonishment and, after a few minutes more, the lady sitting next to me whispers "Can you understand a thing he's saying?" Gradually - thankfully! - it all starts to sound like real words.

And the words, care of first-time playwright Eugene O'Brien, are strong indeed. What is this knack so many Irish playwrights have of making such simple language sound so colourful, of making prose read like poetry? Whatever it is, O'Brien - like his director and fellow playwright Conor McPherson - has it. Through his script and few well-trained glances, Billy and his neglected wife Breda (Catherine Walsh) conjure up a whole town of distinct characters - Feggy, Mouse, The Skunk, Jennifer Collins ("just this morning back from Australia") and a host of other Irish names I couldn't attempt to spell.

Both Billy and Breda want to feel wanted and neither does. Breda, formally nicknamed Pig-arse, has "made the effort" and lost the weight, but it's clear Billy's problems are more about self-loathing than sexual desire. It's a small story but beautifully delivered by this pair of Irish actors, who originated the roles at the Dublin's Abbey Theatre. Walsh even won an Irish Times Best Actress award for her Breda, all crossed legs and arms in telling conflict with her words of erotic liberation.

But, for me, it's Wycherley who really impresses. Once accustomed to his accent and manner - halting unease masked by drink, drunkenness masked by a concentrated effort to appear sober - I was utterly mesmerised by his performance. And I wasn't alone. During one of his second act speeches, he takes one of the longest pauses I've ever seen on stage and the entire auditorium, hanging on his next word, sat in complete silence - not a single murmur or cough, not even a sniffle.

On the downside, Blaithin Sheerin's set is off-putting - nice paintings but whatever is all over the walls and floor looks like plywood. Also, for a series of monologues, Eden feels overly long. I would have preferred to tighten it by half an hour and forego an interval.

Still, this is a moving and intelligent piece, a welcome Irish import. And who knew Sunday evenings could be so action-packed? If Eden is anything to go by, London is a slow place indeed compared to Derry.

- Terri Paddock