BOOK REVIEW : Perpetual Motion in a Shifting Triangle : TALKING IT OVER<i> by Julian Barnes</i> Alfred A. Knopf $22, 273 pages

Without slighting the work of Alan Ayckbourne, Simon Gray and a half-dozen other dexterous playwrights, we may now have the ultimate example of their specialty: British drawing-room comedy, Postwar Version.

A word about Postwar Version. It uses a hydroponic drawing-room. Above, is the contemporary chic of manners and customs, below, is all water. The water is full of piranhas. Above, all ironic sensibilities; below, all churning bloody carnage.

This new, quite perfect example is by a novelist, not a playwright. The novelist, Julian Barnes (“Flaubert’s Parrot,” “Staring at the Sun,” “A History of the World in 10 1/2 Chapters”), is known for his witty explorations of some fairly far-ranging metaphysical and literary themes. Here he works as if to show that he too can bring off the tight, murderous and comical British set-piece.

“Talking It Over” certainly shows that he can. His triangle--two men and a woman--is three acute angles in constant shifting balance. As they shift, they cut. It is said that a perpetual-motion machine would be possible--assuming it was made with sufficient precision--were it not for air resistance and gravity. Barnes has made a near-perfect vacuum; and his machine has no gravity whatsoever, though a certain seriousness, along with perpetually pleasurable movements.

The story of Oliver, charming and hollow; Stuart, sturdy and reliable; and Gillian, sturdy, charming and unreliable (or perhaps simply fed up), is told in their plaintive, accusatory, defensive and dissembling voices. They are not just telling their versions, they are telling it to a fourth person who never appears or speaks, but has a decided force, insofar as they all feel compelled to justify themselves to him (or her).

Oliver and Stuart are chums since their school days. Oliver, handsome, snobbish and interminably witty, goes on to Cambridge. Stuart, tubby, nerdish and straightforward, goes to work in a bank. High-flyer and low-flyer or, as it seems to develop, grasshopper and ant. Stuart progresses steadily while Oliver, for all his erudition and savoir-faire, bumps along from one seedy language school for foreigners to the next. He tends to seduce the students.

The careful Stuart meets the apparently careful but actually formidable Gillian through a singles service. She is won over when she goes to dinner at his apartment and finds a detailed timetable for preparing the meal, ending with “8:30. Gillian arrives!!” (“Those two exclamation marks really did me,” she relates.)

Oliver is introduced and the three become inseparable through a long summer; with Stuart and Gillian as the loving couple and Oliver as live-wire friend and wit. Here, as periodically, the three voices come together to diverge. Stuart remembers the summer as perfection, Gillian complains that Oliver was unnecessary and in the way and what Oliver remembers is: “I was brilliant.”

At the ensuing wedding, Oliver misbehaves and falls to pieces. He cannot bear to be out of the picture. So he falls passionately in love with Gillian, artfully seduces her, wins her away from Stuart and marries her. It is Stuart’s turn to go to pieces, to misbehave at the second wedding, and then to take on Oliver’s wildness. It is Oliver’s turn, moving to France with Gillian and settling down, to become careful and relatively cautious.

The shifts and reversals are infinitely more complicated and numerous than I have outlined to this point and they continue on well past it. What is impossible to suggest, except by asserting, is Barnes’ almost magical skill in making his three-part counterpoint work so well. Each of the three voices catches us, holds us and relinquishes us. Each character alters as it revolves and alters back, sometimes with hilarious sharpness and sometimes hazily. Gillian is an elusive but hardly still center; the two men gyrate frenetically, defining themselves and never getting it right. It is like two populous planets churning around a still moon that is edging along her own quiet course.

It becomes increasingly clear, of course, that Oliver’s and Stuart’s true obsessions are with each other. At one point, a crass and comical outside voice is introduced to assert that they are half-consciously in love. In Barnes’ kaleidoscope, that is only one more colored piece that shines, tumbles aside, and returns.

The book is full of small mysteries that successively resolve themselves and promptly give birth to new ones. The steady mystery that never is resolved is who the silent listener is. Assuredly, it is not God. Perhaps it is the concealed electric wire that snakes out behind all such perpetual-motion machines, and keeps them moving.

Next: Elaine Kendall reviews “Acts of Contrition” by John Cooney (Crown Publishers).