Som ew here, surely, there exists a support group for the many, many Irish acts, who, in the post-U2 glow of the late 1980s, were snapped up by major labels only to get unceremoniously dumped one ill-starred album later. Of these, Lir, the much touted and greatly adored Dublin band of the 1990s, can point to any number of cruel twists of fate: cruel, certainly, but perhaps not so unusual.

Attendant Lir mythology sounds a familiar tune. Early gigs were frequented by A&R men but it was not to be. The initial press response to the North American tour was positive but it was not to be. The Chrysalis imprint came a’calling but it was not to be.

Were they victims of a conspiracy, of crooked management, of the liquid and smoking blandishments of rock?

The truth, as recounted in Good Cake, Bad Cake: The Story of Lir – a fascinating new documentary from Shimmy Marcus – is far more complex and convoluted than any of these potential pitfalls.

“There’s so much about their career that could be any artist’s career,” says the director. “There’s a constant sense of battling against the tide. Maybe the next song will be the one that hits; maybe the next album. The truth is – and you have to understand this going in at the start – that no matter how good you are or how many things you have going in your favour, the chances are you'll never make it.”

Marcus, a film-maker whose keen eye for rock margins gifted audiences Aidan Walsh: Master of the Universe in 2000, has long had connections with the music industry. The sometime director of pop promos for Fun Lovin' Criminals and Snow Patrol was lighting stages at live gigs just as Lir peaked in the early nineties.

“It was Lir. It was Engine Alley. It was so many bands I used to work with back in the day,” says the film-maker. “They’d get a sniff of success and it wouldn’t happen. And for a lot off those bands it was very easy to point the finger elsewhere but harder to turn the mirror on themselves.”

Unhappily for all concerned, finger pointing, in this instance, translated into more than a decade of court action and one greatly delayed documentary. Two years ago, the Good Cake, Bad Cake premiere was pulled from the Dublin International Film Festival due to the protracted legal action between the band and their former management.

"I think it was the first or second film to sell out at the film festival," recalls Marcus. “We had expected the court case would be settled by then but it dragged on and our lawyers advised us to pull the film. So we went from this high of selling 500 seats and a sense of momentum building. It was another left turn that was tough on the band.”

Good Cake Bad Cake 's trawl through 25 years of archive footage, sounds and relevant testimonies turns up many such left turns. Founded in Donaghmede in the late 1980s Lir's first line up – Ronan Byrne, David Hopkins, Craig Hutchinson and Rob Malone – were soon trumpeted as a "next U2".

But the intervening years have heaped a litany of indie rock misfortunes on Lir: an exhausting US tour that took up most of the years between 1993 and 1997, a widely publicised falling out with management and any number of personnel changes. Against this, there were rave notices, a sizable cult following and the occasional hit. Tellingly, all the band members continue to perform: Rob Malone has played bass with David Grey since 1999; others maintain small, indie solo projects.

“They don’t know how to do anything else,” notes Marcus. “And that’s what got them through.”

In common with the Metallica therapy-doc Some Kind of Monster , there is a sense that we're watching people talk something through with Good Cake, Bad Cake : "The thing I love about the band is that there almost too honest for their own good," says Marcus. "We live in a world where artists are so protective and protected. These guys speak from the heart. They're sincere. They were really generous with the interviews as well. They probably said more than they thought they were going to say. It was a cathartic experience for them. I think a lot of shit got cleared up."

It's not just the small time angle: Good Cake Bad Cake 's refusal to prioritise narrative over truth makes it quite unlike any rock-doc we've encountered before. There are no convenient grand implosions, only a series of little ones; there's no attempt to turn the chronicle into pie fight between the musicians and their management.

"Maybe it's because I grew up in the shadow of a very responsible documentary filmmaker," says Marcus, the son of two-time Oscar-nominated documentarian Louis Marcus. "But I always took the view that I wanted everybody to have a voice. I did three interviews with the manager David Reilly and gave him right of reply on a couple of issues. It wasn't a legal thing. I just wanted to be fair. The manager was on this journey too even if he wasn't in the van. This was just as frustrating for him. He had an investment in the band too and not just a financial investment."

This is the second time Shimmy Marcus has spent five years on a music documentary " . . . just trying to make sure that it's truthful". His thoroughness is commendable and the finished film is a splendid entertainment even for newcomers to the band. Good Cake, Bad Cake may have taken him away from narrative features and a potential quick follow-up to Headrush and Soulboy but he seems perfectly happy with the idea of putting Lir in front of crowds where they belong.

“It’s that feeling you get when you discover something – a new band, a new sound, a new song – and you drag someone along because you want to share it,” he says. “Lir are a band that built up an audience that way. And I’m someone who wants to drag you along to the show.”