WHO is this man? Where's he been all my life? Am I stupid for never having heard of him? I've stumbled out of a show on to a New York street, and I don't know whether I'm in Glasgow or the Big Apple. Just finished is an afternoon performance of Bright Lights Big City, the novel of cocaine-fuelled eighties life by Jay McInerney, transformed into a musical and played to an audience of 50 in a brick-walled studio theatre.

In the middle of a large cast of all-American singers and actors (think Kids From Fame grown up) was a 40-year-old guitarist with cowboy boots, shoulder-length hair, and long white shirt-tails, his lived-in features a testament to a rock 'n' roll lifestyle (or was it just the three children?), his accent the purest Glaswegian.

His name is Paul Scott Goodman. If, like me, you've never heard of him, take note. You'll hear a lot more in future.

Bright Lights Big City is a stunningly accomplished musical. Where the traditional Broadway show employs a whole team of book-writers, lyricists, and composers, McInerney's novel has been adapted by Goodman single-handedly. It's not just that he's given it a forceful melodic rock score, it's also that he tells the entire story in song. That he also performs in the show, narrating this story of high-living New York hedonists with the voice of an outsider, is more impressive still.

The production I saw was a studio try-out at New York Theatre Workshop, a small Off-Broadway theatre over the road from the famous La Mama Experimental Theatre Club. Low-key the production might have been, but every producer in town had been to check it out. Malcolm McLaren was expected in the audience the next day. And Goodman was being courted by Broadway.

The producers were wise to be there. After all, New York Theatre Workshop was the starting point of Rent, now a major Broadway hit and opening in London on Tuesday. Goodman, however, is taking things a step at a time. Rather than leaping straight to the Great White Way, he's sticking with Theatre Workshop and director Michael Greif (also responsible for Rent). They're planning to mount a mainstage production in February, and only after that will they consider transferring to Broadway.

So how did Goodman get here? His Broadway dream began at the age of five, the day his father took him to The Jolson Story. His parents were members of the Avron Greenbaum Players, the Glasgow Jewish amateur dramatics company, and it wasn't long before the stage-struck lad was taking juvenile parts in the annual musical.

From Hutchesons' Grammar, he went on to Glasgow University, and from there to London, lured by the energy of punk. ''Being in London at that time, and going to see the Pistols and all those bands, it blew my mind,'' he says.

''People could just get up and swear on stage, and that quality has stayed with me.''

His first job was as press agent for Keith Moon, legendary drummer with the Who. Realising he'd sooner be publicising his own burgeoning music career, he handed in his notice three months after starting. By a bizarre coincidence it was the very day Moon killed himself. ''I quit my job, took a walk, and heard on the radio he'd died,'' he says. ''People thought I was nuts, because it was a press agent's dream, but I wanted to have my own press agent.''

Setting out as a singer-songwriter, he and a piano player took support slots for tours with Joan Armatrading, John Cougar Mellencamp, Steeleye Span, David Essex, and the Average White Band. As a would-be actor, he once auditioned for Giles Havergal of the Citizens' Theatre, who commented on how energetic his reading of Hamlet was. It's the same energy you'll see on stage today.

In 1981, the National Theatre gave a small-scale staging to a musical he'd written called Fine Life. Then, believing the US was the place to further his interest in musical theatre, he headed to Los Angeles, and, in 1984, to New York. Since then, he's written seven musicals, and won three major awards, but not without a struggle. To make ends meet he's waited tables, written jingles, and helped out with his wife's business - New York's largest breast-pump rental service for young mothers.

''In the last year or two, my name has become better known, just because people have begun writing about me in New York,'' he says. ''I've been doing my one-man shows for years, but that's the way it works in New York. There comes a point when, all of a sudden, people latch on. Once Bright Lights started happening for me about a year ago, I could just feel this upsurge of interest - people began calling me who wouldn't take my calls before.''

What's refreshing about Bright Lights Big City is that while it observes the rules of traditional song-writing craft - witty lyrics, good tunes, coherent story - its attitude and sound are all contemporary. ''It's not rock in a Jesus Christ Superstar pseudo sub-rock way,'' Goodman agrees. ''I think Rent was the first one to do that. Jonathan Larson, who wrote Rent, used to live round the corner from me, and we used to talk about how we wanted to write musicals, but we'd been brought up with rock 'n' roll, and we'd played in bands.

''Andrew Lloyd Webber knows what the chords are, and he knows how to structure a rock song, but he never played in a rock band. The difference is not in the structure, it's just that we've been there.''

So will he return to save the Scottish musical? ''One of the projects I was considering for my next show was the Harry Lauder story,'' he says. ''I don't know why musicals have never come out of Scotland. I grew up going to pantomimes, which to me is a great musical theatre form.

''If there are any Scottish entrepreneurs who want to commission me, I'd be happy to write a Scottish musical.

''I thought about writing one about Celtic, because I've been a life-long supporter, and I could combine the two passions.

''It's about getting the right story. If you could get someone like Irvine Welsh to write a plot for a musical, that would be great, because it would come from somewhere honest.''

Are you listening, Irvine?