There are huge changes afoot in Kate Thompson's life. Tomorrow her first novel, It Means Mischief, will be launched in the Abbey Theatre. The next day she will film her final scenes of Glenroe, bringing the curtain down on a nine-year run of playing femme fatale Terri Gilleen. Then the wrap party and then, at last, a rest.

After two years of combining acting and writing with bringing up her 11-year-old daughter Clara, she needs it. She will escape to the west for a break and then begin to think about life after Glenroe.

"The one thing I am certain of is that I will keep writing. But I absolutely hope to keep acting as well. I would love to get back to the theatre and do more stage work. Above all I want to play a different character now. I've been playing Terri for nine years now and I do worry about becoming so tangled up with her that people can't tell us apart." In fact it is hard to imagine anyone more different from Terri Gilleen than Kate Thompson. Perched bolt upright on the edge of a sofa in Dublin's Shelbourne Hotel, dressed in blue jeans and a baggy brown suede shirt, her candid blue eyes light up when I point out the dissimilarity.

"No, I'm not at all like her. Terri is the type of person I wouldn't even want to invite around to my house. Thankfully my friends always say that they can never believe it's me on the television, I'm so unlike her." Kate was brought up in Belfast but came to Dublin to study English literature at Trinity and it was there she met her husband, actor Malcolm Douglas. Soon they were engulfed in the schedule of two busy actors with a small baby. In the midst of it all, Kate won a best actress award for her part in Mary Elizabeth Burke Kennedy's adaptation of George Moore's The Trial Of Esther Waters. Then there was Glenroe as well as the constant bedrock work of voiceovers.

Glenroe has been good to Kate Thompson and she will be very sorry to leave it. There is a wonderful family atmosphere about the show but something clicked in her mind as she was coming up to her tenth year in it and she decided it was time to make the break.

"Glenda Jackson once said that acting is like any other job but that once every five years something happens which reminds you of why you are an actress. Of course that does happen, but luckily for me I have discovered something else I really love doing and that is writing."

The writing bug came upon Kate in a most inauspicious manner. Several years ago she began to wonder was there anything else she could turn her hand to which would provide her with some security. She wrote several short stories which she says were horribly pretentious. Then she turned full circle and wrote off to Mills and Boon for their brochure. Following their guidelines, she embarked on a novel. By chapter three she had strayed well away from the Mills and Boon formula and was really enjoying writing. By the time Mills and Boon rejected her work she was already hooked.

It was Malcolm who put the lid on it. Two Easters ago they sat down to discuss the feasibility of Kate managing to write a novel despite the demands of their hectic lives. Malcolm told her it was probably a long shot but that he felt it was worth a bash and to help her he would take care of all the domestic responsibilities in their house in the Liberties. It was a generous offer and one which he has honoured to the letter.

"Malcolm and Clara were both fantastic. Every evening, Malcolm read through what I had written and made suggestions. He was always spot on and now I know to take his corrections on board without even hesitating. As for Clara, in the beginning she couldn't understand that even though I was at home, I was still working and couldn't be disturbed. She would hover around the computer chattering to me. But eventually she got the message. Now she has taken to writing her own novel which causes a few battles for access to the computer. Luckily Clara's writing is pretty sporadic."

It Means Mischief follows the trials of a young actor at the start of her career on the Dublin stage, working her way through a minefield of vicious casting agents, catty fellow actors and amorous leading men. Not surprisingly, everyone she knows in the business has been asking her whether they are they in the novel. But Kate insists that all the characters were born entirely of her own imagination.

"In fact writing the whole book was just like having a baby. I used to hear myself describing to my friends the conception, the gestation, the labour and the post-partem depression and think, what am I doing? But I really had all those symptoms. The day I finished It Means Mischief I sat down and cried."

Of all people, novelist Deirdre Purcell knew exactly what Kate was going through and it was to her she turned when she got really despondent about the book. It was Purcell who she asked to read the first draft of the book and Purcell who chose the title.

"I cringe when I even think of the first draft it was so bad. After I had finished reworking it I rang up everyone who I had asked to read it and apologised for inflicting it on them. But the people who read it were very kind, I suppose there must have been something in it for them to believe I could do it."

In fact, it was the prospect of her mother-in-law reading the book that made her most nervous. She tentatively broached the subject of the sex scenes with her well before publication only to be told "don't worry dear, I'll have a read and correct them for you". But it was only after she sent the book to the publisher that the self doubt really set in.

"Above all I was worried about wasting Malcolm's time and wasting Clara's time. Also as an actress I was used to constant feedback, with a director talking me through my performance. So waiting to hear from the publisher was something I wasn't prepared for."

Kate has now finished her second novel and has begun work on the third. She is looking forward to a reprieve from the punishing schedule of the past two years and to establishing some kind of routine.

"I was just wrung out after working 10 and 11-hour days. Sometimes I would work to the point of exhaustion and then keep on working beyond it. Now I am dreaming about a working day that starts at 11 and finishes at five."

Slowly Kate and Malcolm seem to be drawing closer to a long-harboured dream. "It may seem very odd but Malcolm and I have always longed to live in the country and raise cats. We saw a cattery once and since then it has been our fantasy. I know that I could be very happy in the country."

As for Terri Gilleen, Kate is very cagey about her fate but promises two cliff-hanging episodes at the end of the series. More she will not say.

It Means Mischief will be published tomorrow by New Island Books. Price £6.99.