You hear it before you see it: a loud pulsating thrumming that presses up against the door of the rehearsal room and sounds like the rhythmic pacing of some very large animal. Open the door of The Factory's rehearsal room and the animal is revealed to have 24 feet - the 12-strong male chorus of the latest new dance-show, Dancing on Dangerous Ground.
Right, so. First there was Riverdance - starring Michael Flatley and Jean Butler. Then there was Lord of the Dance - starring Michael Flatley, accompanied by, said many pundits, Flatley's ego. Now it's Dancing on Dangerous Ground, starring Jean Butler and Colin Dunne, himself an ex-Riverdance lead in one of the global production's many subsequent incarnations.
Butler is striding around the rehearsal room, directing the timing of the 24 pounding feet. "It's got to be like, dead on!" she insists. The feet of the Fianna beat obediently, responding instantly to any changes in direction, their reflections thrown back a dozen times by the mirrored walls.
Dancing on Dangerous Ground is based on the legend of Diarmuid and Grainne, with Dunne and Butler playing the central characters. In addition to dancing the lead parts, they have also jointly choreographed and directed the show.
At the lunch break, Butler drinks coffee, and smokes the ubiquitous dancer's cigarette. Yes, it's all true, she does have legs like Barbie prototypes stopping somewhere near the ceiling, and she has quantities of natural grace that commands the eye even if she's simply walking across the room.
It's the last day of a 10-week rehearsal period in Ireland, before the production transfers to London in the run-up to its December opening at Drury Lane.
So, what's this about Jean Butler dancing again? Didn't we hear she had got fed up with the dancing and wanted to be an actress? What happened?
"I just never got the gig," she explains, straight out. "I got loads of auditions, I got called back three or four times, but I never got the job. I wanted an acting job, but it never happened. And there came a point where my agent sat me down and talked to me and I thought: Is the rest of my life going to be about waiting for a break in cinema?"
She did actually get the gig in Terence Ryan's The Brylcreem Boys, which bypassed cinema and went straight to video here, having collected some dire reviews along the way.
At about the time Butler was taking a hard look at her cul-de-sac film career, the idea of a collaborative dance show was broached by Colin Dunne. It was Christmas time, 1997. "The two things happened at around the same time," she agrees. Since they both had had first-hand experience of the Riverdance phenomenon, both were uniquely qualified to explore the idea of creating their own dance-show.
They kicked round various ideas. "We tried to write out own story, but that didn't work - we're dancers, not writers. Gabriel Byrne and Patrick Bergin both pitched in with ideas - they're people who don't live in Ireland all the time, so they have an outside view on things. They pointed us in the direction of legends."
Dunne and Butler holed up in a cottage in Wicklow for a weekend, and read their way through the drama and set-pieces of Irish legends, before settling on Diarmuid and Grainne. "Love, marriage, feasts and funerals," explains Butler. "Lots of scope for big visual set pieces."
Once they had decided on the story, they shared the choreography more or less equally. "It wasn't a question of `This is my scene, so I'll do this bit and you do that bit'. It was more that we each worked alone on something - then the other would come in and cast an objective eye over it and fix anything that wasn't working." It sounds like an unusually compatible working relationship.
"Colin and I both have the same vision and sensitivity to Irish dance," says Butler. "What makes this different to Riverdance is that the lead dancers and producers are the same people." What about Lord of the Dance - didn't Michael Flatley do something similar to what they're doing now?
She takes a big breath. "Riverdance happened. It was brilliant. I personally couldn't have taken on this show without having had the Riverdance experience. Then Lord of the Dance happened, and basically launched Michael Flatley, and his interpretation of dance: it was a vehicle for him alone, rather than for the dance itself."
Butler admits that the input of so much creative energy - and, presumably, the pressure of coming up with a show which will inevitably be compared to the other two big dance shows of this decade - has been exhausting. "It's been hell!" she says frankly, and burrows for another cigarette with a grim expression. Would she do it again? "If I do it again, I certainly won't be in it. It's so hard to distribute all my energy to the company - and I have to focus on my own dancing too, of course."
It will cost in the region of £1.5 million to stage Dangerous Ground in London, with music by Seamus Egan. They have impressive backers, including Harvey Goldsmith, who promoted Live Aid, and Radio City Entertainment in New York - the show will transfer there in March.
Both Bulter and Dunne have also invested their own money in the production, which has now been in development for almost two years. They hope for an 18-month run, which may end in Dublin.
"It's scary. It's exciting. I'm stressed." There are a few pauses in the interview, while Butler smiles, and struggles vainly to remember details: a name, a source for an idea, a transfer date. "My brain is scrambled," she admits, adding that she's not sleeping well at the moment.
One of the pauses comes when asked to sum up Riverdance in one word. "I'd need too many words," she says eventually. How about Lord of the Dance in a couple of words, then? "They would have to be two really diplomatic words," she says dryly. "Can I come back to that?" she says. But funny enough, she never does.
Dancing on Dangerous Ground opens at the Theatre Royal, Drury Lane, London, on December 6th and runs until February
