Conor McPherson writes in a programme note that when he first conceived his 2001 play Port Authority, it “didn’t seem to bother with a plot, or try to make a point… It just came along like a song you might catch or perhaps ignore. But I couldn’t ignore it.”

This description applies equally to the finished article; lyrical, haunting, but lacking in narrative structure.

Three Dublin men - one young, one old and one somewhere in between - sit in solitude and tell tales of regret, missed opportunity, and mistaken identity.

The youngest, Kevin (Andrew Nolan), has moved into a house-share where one of his new roomies also happens to be the love of his life. Meanwhile middle-aged deadbeat Dermot (Ardal O'Hanlon) finds himself swept up into a jet set world after being invited to the home of a wealthy financier. And Joe (John Rogan) is prompted to recall an unfulfilled romance by the delivery to his old people’s home of a mystery package.

As dramatic set-ups go, it’s about as simple as one can imagine, giving McPherson’s writing full space to breathe. And in the echo chamber that is the Southwark’s Vault space, the tuneful nature of the lines is emphasised effectively.

But the lack of interaction places big demands on the actors, and it’s in this that the production flounders. O’Hanlon is of course the major draw, having risen to stardom via Father Ted and a successful stand-up career. Sporting shaggy hair and beard, he captures Dermot’s wide-eyed naivety (a quality he can portray better than most) but not the full depth of his loneliness and despair.

Likewise, John Rogan has an endearingly light touch with Joe, a man whose memories of loving wife Liz are tinged with regret, but too often draws a blank when he should deliver a knock-out blow.

It’s down to Andrew Nolan to provide the piece with much-needed heart, though unfortunately he has the tale that contains the least. Nevertheless, he lends a welcome fluidity to proceedings and is the performer with whom it’s easiest to relax (his colleagues dropped a few too many lines on opening night).

Tom Attenborough’s production is neatly staged with crates in place of the usual bench, and atmospherically lit from all angles by Joshua Carr. But the joy of this play lies in the music of its language, and this trio isn’t quite in tune.