QUINX; Or The Ripper's Tale. By Lawrence Durrell. Viking. 201 pp. $15.95.

READERS OF the four previous novels of The Avignon Quintet will be compelled to go on to Quinx, which completes what Lawrence Durrell calls his quincunx: an arrangement of five objects so placed that four occupy the corners and the fifth the center. Durrell's admirers should prepare -- after the fairly straightforward narratives of Monsieur, Livia, Constance, and Sebastian -- for an exuberant potpourri of conflicting themes and vignettes, dozens of characters, and a plot that

builds to what is, finally, an inconclusive end. Those who have not read the four previous novels probably need to do so.

Like his 25-year-old Alexandria Quartet, The Avignon Quintet displays Durrell's masterly, and masterful, artistry -- as well as his preoccupation with the sexual act and its relation to unattainable love, a preoccupation that goes back 50 years to The Black Book. But even with the other four novels framing it, Quinx is frustrating. Most annoyingly, the quintet's plot has been usurped almost entirely by abstract musings about how to make The Novel.

These speculations seem no more integrated with the narrative for having been shoved into the mouths of the characters Aubrey Blanford and Robin Sutcliffe, two novelists who create each other, each the other's doppelganger. (Who created whom becomes intentionally unclear.) Here is Blanford, repeating "to his own mind, 'I dream of writing of an unbearable felicity. I want to saturate my text with my teleological distress yet guard its slapstick holiness as something precious. To pierce the lethargy, indolence and distress of my soul.'" One wishes Durrell actually had done in Quinx some of the provocative things his characters keep suggesting a novelist can, and should, do.

In Quinx the plot of the quintet jerks to an anticlimatic finish. Lord Galen leads a long search for the Templar treasure, a cache -- buried in Avignon during the 14th century by the heretical Knights Templar -- that just might include the Holy Grail. A host of love- crossed characters joins him in his obsessive quest, which runs from just before until just after World War II, primarily in southern France. The characters' search for the treasure becomes as labyrinthine as their attempts to find love.

Constance, a central figure whose actions are the most intriguingly detailed, exemplifies the connection. Her husband Sam dies in the war. In Nazi-occupied France, she goes on to an affair with Prince Affad, also known as Sebastian, a member of a Gnostic cult that seeks the Templar treasure. Unfulfilled, Constance yet finds purpose in plotting to prevent Sebastian's ritual murder by the cult while treating (she's a psychoanalyst) his autistic son -- and while having a lesbian affair with another of her patients, the mad Sylvie. Eventually, Constance meets the blind German General Von Esslin, to whom she goes for information about her dead sister Livia. Mistaking her for his own sister Constanza, Von Esslin befriends her and leads her to the wartime double agent Smirgel, who has had an affair with Livia -- and who owns a map to the Templar treasure, which is buried in a "quincunx shape of . . . caves." Smirgel exchanges the map for Lord Galen's promise that the British will not prosecute him for war crimes. Finally, the treasure within reach, Constance and Blanford tentatively admit their love for each other. Constance's complexly ambivalent and salacious affairs, spread throughout the quintet, clearly tie in with the labyrinthine search for hidden treasure.

CERTAINLY, Durrell uses the Templar treasure plot mainly to fuel the complicated relationships which he delights in unfolding. And he employs the scheme of multiple narrators as writers of novels within (and of) his own novel throughout the quintet. But in Quinx, the pretext of the plot's importance fades. And the once subtle narrative techniques grow obtrusive and silly. Durrell makes a joke out of the very things he took seriously for 1,400 pages. At last, just when the Templar treasure becomes as fascinating as it is near, Blanford transforms any discovery into the abstract "thought that if ever he wrote the scene he would say: 'It was at this precise moment that reality prime rushed to the aid of fiction and the totally unpredictable began to take place!'"

In Quinx, Durrell seems most of all to be exploring the Idea of the Novel. But he fails to do so by means of his characters. As Constance, much less individuated than previously in the quintet, is made to explain: "'We exist in five-skanda form, aggregates, parcels, lots, congeries. They cohere to form a human being when you come together and create the old force-field quinx, the five- sided being. . .'" She has been made a mouthpiece, as have the other characters, for Durrell's abstract expressions. Anyone in Quinx could have said Constance's, or nearly anyone else's, lines because all the characters' voices are similar; when they are not similar, they are the same. Durrell's names are interchangeable.

The Writer is a despot in Quinx. Narrative technique, plotted through characters who seek hidden love and treasure, has been reduced to a private jest. Durrell did not have to stop developing his plot and his characters to make the point that both love and treasure may be unattainable. Quinx possesses more of Durrell's flat assertions than it does of his elegant art.

Of course, the subtitle is "The Ripper's Tale." Durrell slashes his characters into shreds of frivolous dialogue about what a grand writer can or should do, instead of doing it himself. He has his laughs, and loses his story.

In the end, though, Quinx's faults hardly matter. Lawrence Durrell may have failed to bring off the final volume of The Avignon Quintet, but he remains a writer whose novels will be read as long as people care for books.