Stir-fry by Emma Donoghue Hamish Hamilton $170 REVIEWING first novels can be a revelation or a nightmare. There's nothing worse than that sinking ''how did this person get published?'' feeling by page two and that certainty that here's a book destined to sink without trace. Happily Emma Donoghue's first falls into the category of revelation: here is a wonderful new talent. I'm already looking forward to her second. Donoghue is, at 24, not an unpublished writer, however. Her play, I Know My Own Heart, has been produced in her hometown, Dublin, and in Cambridge, where she worked on her thesis on 18th-century literary friendships. Last year her book Passions Between Women: British Lesbian Culture 1668-1801 was published. There's a direct link between that worthy-sounding tome and Stir-fry , which also has lesbianism as its central theme. Seventeen-year-old Emma Murphy, new in Dublin, new at college, newly left home, answers a college notice board advertisement for a flatmate: ''Two seek flatmate. Own room. No bigots.'' ''Would you have any idea what exactly the wee symbol stands for?'' she asks a classmate, who warns the women will be ''fairly feministy, you know the sort''. But Emma doesn't know. A virgin, she knows little of the world and even less of lesbianism. So when Jael and Ruth show her their shared room, shared bed, she doesn't realise what they deliberately avoid telling her. She moves in and as she tries to find her way in this new world, the warmth of the flat and the two women envelops her. But their home becomes more than a retreat. Learning their secret by accident, she must confront her feelings about it, about them and about her own sexuality. She struggles with issues familiar to any young woman or woman who remembers being young: fancying a man who doesn't fancy you; wondering whether men and women can just be friends; throwing herself into a tedious pastime to avoid all those difficult thoughts. It's a sensitively written, compassionate and entertaining story that never becomes mawkish. It doesn't try to convert and brings no message except perhaps to say: ''Don't close your mind to life's possibilities.'' That it should be saying so in Ireland with a cast of, inevitably, Catholic characters, makes that all the more poignant and emphatic. For all that, this is a light book with a natural flow, a book to laugh at, to read fast and with pleasure, and to admire. That it should come from such a young writer, yet one with such insights and such a wonderful turn of phrase makes it all the more admirable.