Fidelity, now there's a word to conjure with. And its opposite, even more so. If Ms St John needed a sub-title for her latest work, then "Sex, Lies and Seduction in Belsize Park" would be a good one. It is in that well-to-do area of North London, incorporating Golder's Green, Hampstead and the aforementioned Belsize Park, that she sets her comedy of manners, her cast-list of conniving husbands and career-driven, oblivious wives being numbered among the professional classes.
Alex and Andrew have been friends since their Oxford days, Alex now a journalist, Andrew a teacher. They have not met for years, mainly because Andrew has been living in America. Then, one night at a party, their stars bring them back into conjunction once again. Not alone that, but Alex also spies Barbara with whom he had a fleeting affair some two years before.
Married to critic Claire and with two children, the "brats" Marguerite and Percy, Alex again falls under the spell of footloose and fancy free Barbara. She is the complete antithesis of his coldly ambitious wife, with whom he has not slept since the birth of Percy, who is now six. Barbara, that golden brown, voluptuous girl, is a drifter, holding down jobs only when and if she wishes, and at present she is keeping house for lawyers Tom and Serena and their twin sons, the "heavenlies" James and John.
Andrew also has marriage problems, his wife refusing to come back to England with him and retaining possession of their seven-year-old daughter, Mimi. He too falls under the spell of unsettled Barbara and has a liaison with her that ends up in bed. But Barbara still has a crush on Alex and, inevitably, they also get back together again.
However, Alex will not leave Claire because of the children, wishing as he does to give them a settled family background to grow up in. But the children - as drawn here a bit too grown-up and observant for their ages - are well able to perceive the situation between their parents and live in a constant state of anxiety that a divorce is imminent.
Eventually Barbara, as is her wont, packs a suitcase and sets off for India with another misfit called Gideon. Although now off-stage, she continues to haunt the fevered imaginations of both Alex and Andrew, who view their empty lives ahead of them with a mixture of anguish and joyful pain.
Ms St John is an expert at chronicling the unrelieved resonances that dimple most of our lives. Her people are becalmed in the social fabric, free-wheeling when they should be pedalling furiously. They are eminently civilised, they fill in their days with work, play and socialising, they refuse to disrupt the veneer of the expected.
But now and then a rip appears, a line in the sand is stepped over, a minor breach in the barricade attempted. Invariably this glitch is of a sexual nature, and again, invariably, to preserve the modus vivendi, this small mutiny is layered over.
Using the light touch of nuance and a bending rather than a breaking, Ms St John traces the pained awkwardness of such encounters quite expertly. Nothing very much happens in her novels, certainly outwardly. Mostly it is thought that is clandestine, her middle-aged men and women savouring the spirit of the betrayal rather than the physical act. And her dialogue shows off an expertise in the art of prevarication, with its stops and starts, its repetitions and broken sentences, that is a model of its kind.
Vincent Banville is a writer and critic