Edinburgh-born Sara Sheridan has just published her first novel, a thriller entitled Truth Or Dare. The original, working title was Scaring The Protestants. The novel centres on the fallout from the IRA murder of an English woman, and is set in London, Glasgow, Belfast, Dublin and Galway.

Sheridan spent five years living in Ireland. Three of those were spent in Dublin and two in Galway. "Mum and Dad were rooting for me to go to Cambridge, but I read The Beastly Beautitudes Of Balthazar B and decided to check out Trinity College, Dublin instead. I flew over for the weekend and met J. P. Donleavy at a bus stop. I was sold, so I applied and got on to the English Literature course."

During her time at Trinity, she wrote a column for the Dublin Event Guide, and also had a part-time job helping to restore a tumbledown Georgian house on Mountjoy Square. Then she met her future husband, Seamus, in a nightclub. "We mortified both our families by getting married, after which we ran off to Galway." She was 21.

At that time, the beautiful stone building that is now called Nimmos, behind the Spanish Arch, was "just a shell". They rented it for a year and a half, and ran a restaurant there, called The Blue Raincoat. "We also used the walls as an exhibition space. During the Galway Arts Festival, Circa magazine would run a print competition and we'd display the prints."

Her husband did the cooking and Sheridan was front of house. "We used to fish out the window. At night, we'd watch the swans go by, so many of them they made the water seem luminous."

All this time, she was continuing her studies at Trinity, although in a cheerfully unorthodox manner. "When we were living in Galway, for the last two years of my degree, I didn't go to any lectures. But I read. And I wrote my essays - sitting up late at night between 1 a.m. and 2 a.m. on top of the freezer in the restaurant." She hitch-hiked up to Dublin for the final exams. She got her degree.

With the imminent birth of their daughter, Molly, they left The Blue Raincoat and Galway behind. "Running a restaurant and gallery was a wonderful experience, but we didn't make a penny. We were so young, barely in our twenties. We figured afterwards if we'd charged even 10p more for every cup of coffee we sold, we'd have made a profit," she sighs.

The couple moved to Edinburgh, where Sheridan's family is all based. Now 29, she is divorced from Seamus.

"I figured out that I couldn't work full time, look after a flat, myself and a baby, so I quit my job and started to write," she says. "I decided that I'd give myself two years to write and if I wasn't making money out of it by then, that I would give up."

She wrote 50,000 words of what will be her second novel, The Plea- sure Express, and sent it off to "about 100 publishers". They all turned the unfinished draft down, but a few wrote back encouraging letters, saying they'd be happy to look at something else. She went on to write Truth Or Dare in four months. It subsequently went to auction, with four publishers bidding for it. In less than a year, Sheridan had achieved what she had hoped to do in two years. "People are always telling me I can't do things. And then I do them."

She relates this to me in her home city of Edinburgh, from under a nimbus of thick, dark hair. Truth Or Dare has been published in that increasingly popular format for first novels: as an original paperback. The initial print run has already sold out, clocking up an impressive 20,000 sales.

Less than a month after first appearing on the bookshelves, it's being reprinted - wildly welcome news for any writer, and especially so for a first-time novelist. Foreign rights have already been sold to Germany and The Netherlands. There is also interest from three companies for the film rights of the novel's screenplay, which she has also written.

However, Sheridan stonewalls me completely when I ask the obvious standard question of how much she received for Truth Or Dare. "Why should I tell you that? Why would anyone tell someone how much they've earned?" she says, seemingly genuinely affronted. "That's something private, my own business." She reveals only that it was "a very good offer. And yes, I've been making enough to support myself with my writing for the past two years now".

The central character in the novel, Liberty (Libby) Lucas, is from Belfast. Why did Sheridan choose to make her Irish? "Well, I'm Scottish. I know what it's like to live in a place where there are two conflicting cultures - Scottish and British. And I wanted to write about a character who had been through a terrible injustice, which is true of so many people in the North."

Libby has left Belfast because of deadly reaction to an installation she made as part of her architectural degree. In a park off the Ormeau Road, she built a maze in which the colours of the walls flipped over like the ads on roadsites. The maze was inspired by the coloured kerbstones that traditionally mark out hardcore Protestant and Catholic areas. The resulting publicity led to her family home being petrol-bombed; there was a gas explosion and both her parents died. Libby goes to London, to try to start afresh.

Once Libby and her new-found friend in London, Becka MacIntosh, stumble on to the darkness created by an IRA murder, they go on the road to try to avenge the death. The book's blurb reads: "They break the rules. They make up their own. They lie, cheat, steal and panic in equal measures. Drink, drugs, bleached hair and bad disguises. Female friendships, families . . . and premeditated murder."

With intricately-planned novels such as crime or thrillers, attention to facts is essential to the believability of the plot. And while truth may often be weirder than fiction, some of this fiction is very weird indeed. Truth Or Dare is a road-romp of sisterhood with a hell of a lot of potholes along the way.

Sheridan has never lived in Belfast and says she did a lot of her research by reading material from Amnesty International. There's a scene in the novel in which Becka goes into an RUC station in Belfast to report a murder and give information about the men who were responsible. "Becka emerged from the building just over an hour later. They took her information and just let her go." Factually, this is so far off the mark from what happens in such situations that I ask Sheridan how she researched this particular scene.

"Well, I've never been in an RUC station, so I wouldn't know personally, would I?" She says: "I needed to get my characters down to Dublin. It's like telling a story in a pub. You can't let the facts get in the way of a good story."

Sheridan has just completed a second novel, The Pleasure Express, about a call-girl in Hong Kong. Comparing Truth Or Dare with the new book, she says: "I think reading Truth Or Dare is like eating a really good burger and chips. It fills you up. But The Pleasure Express is like a three-course meal by a chef who knows how to make sauces." The burger and chips is waiting to be served up to you at bookshops around the country.

Truth Or Dare is published by Arrow, price £5.99 in the UK