Young Liam Wilson is pretty cool, but it’s not quite enough: he does OK, but there is always someone a little better. And then he’s startled by someone new at his school, also called Liam Wilson but just that bit better-looking and more confident. It’s an intriguing launching-point for this one-man rollercoaster ride through the seamier side of Dublin life, as Liam seeks the magic he feels his life lacks.

The storyline is reminiscent of Dostoevsky’s The Double, when a dull young man is confronted with a doppelganger who is much more confident and successful. Though Liam comes from a financially comfortable family and has a lot going for him, sometimes he thinks mediocrity would be better than being almost great – so when confronted by the second Liam, he tellingly announces that he’ll take the more prosaic diminutive Billy to avoid confusion.

From then on they are friends, but Liam is always cooler, more adventurous and rebellious; over time their paths diverge, only to re-cross as Billy hits crucial points in his life. He still feels as if he is one of those people without music and poetry in their soul, until he discovers poker (through the mysterious Camilla in a perhaps overlong detour in Budapest). From then on Billy is hooked, seeking excitement in the danger of high-stakes games and taking more and more risks.

The performance by Edwin Mullane is chaming and he has no problem keeping our attention for the hour he is on stage, though occasionally he stumbled over lines – understandable early in the run, there are a lot of words. He plays Billy as an almost-likeable raconteur, but perhaps it needs just a little more light and shade: the tone of world-weary wise-guy perplexity is fairly constant. I liked the design with hanging playing cards, which give alternative focal points, and the ominous sound design is so simple yet very effective, though I did wonder why Billy was so down-at-heel in his appearance. Maybe a nice silk kimono rather than the tatty dressing gown?

Even allowing for the accents and setting, it fits the classic tradition of Irish storytelling in the rhythms and personality of the piece. It’s the occasional cliched anglicism that jars – phrases like black dog, whiff of cordite – whereas the local slang, sculling your drink or giving someone a clatter, enriches the experience.

The ending is surprising. Perhaps the clues were there all along and it is satisfying to see them click into place, but that does not make it easy; it’s a concussion of a conclusion that pulls the threads of the story tight, and leaves you thinking as you walk into the night. There is enormous promise in this play, and it would be interesting to see it by the time it is established in its Edinburgh run, benefiting from a little tightening of the script and a really slick performance.