A Day with Picasso: Twenty-four Photographs by Jean Cocteau.

August 12, 1916 was a mild day in Paris, with bright sunlight shadowed intermittently by cirrus clouds. It was a day that Picasso chose to dally with nine friends, some old and some new, in the cafes of Montparnasse. It also happens to have been a day when Jean Cocteau, a new friend, joined the bande and brought along his mother's Kodak.

Thanks to the sleuthing of Billy Kluver, an engineer who participated in the art and technology experiments of the '60s and has recently devoted his talents to describing the glory years of the Left Bank, we know exactly when these twenty-four photos were taken and apparently everything this crew did. Kluver has gathered the full meteorological picture of that day, tracked the path of the sun and graphed this data onto the two rolls of photographs Cocteau exposed in order to determine exactly when, where, and with whom they dallied.

It is an amazing feat of detective work, and Kluver does an excellent job of identifying the members of the party and sketching the roles they played in Picasso's life: the poets Max Jacob and Andre Salmon; artists Moise Kisling and Amedeo Modigliani; art critic Henri-Pierre Roche; plus a bon vivant, Manuel Ortiz de Zarate; a fashion model called Paquerette; and another artist, Marie Wassilieff. The ninth, of course, was Cocteau, who wielded the camera.

But the real story lies beyond the idyll recorded in the photos. Picasso and his friends were resting in the eye of a hurricane. On that day, the First World War was over two years old and approaching the midpoint of its terrible duration. Almost from the beginning, the war had radically transformed the lives of European avant-garde artists.

Picasso's greatest friends were not in these photos, and they were not free for lunch. Both Georges Braque and Guillaume Apollinaire were struggling to recover from injuries they had already suffered in the fighting. Earlier that year, while serving in the trenches, Apollinaire had received a head wound that would lead to his death in November 1918. In 1915, Braque had taken shrapnel in the head and undergone surgery, but he was lucky enough to survive and finally return to health.

In fact, the war had shattered Picasso's intimate circle and vaporized the social, material, and intellectual supports that were finally beginning to make the twentieth-century avant-garde an international success. Only a few months before the war began, an auction of a collection called "La Peau de L'Ours," which included the work of Picasso and Matisse, had brought worldwide fame and financial rewards to these two artists. Picasso's established relationship with his dealer, Daniel-Henry Kahnweiler, was about to result in exhibitions in New York, as well as across Europe. Picasso was being noticed by the world of high fashion and even by some aristocrats. It seemed that he had finally arrived. Then came the war, the collapse of the art market, the exile of Kahnweiler (a German citizen), the loss of public attention, and the departure of his buddies for the front. Picasso's lover, Eva Gouel, soon began to fail from cancer (she died a few months before the photos were taken). As a final kick in the stomach, a number of vociferous critics had begun to scream that Cubism was a German plot to undermine French culture.

On August 12, 1916, then, Picasso had been lying low. As a Spanish national, he could not be drafted, nor did he choose to volunteer (as Apollinaire, an Italian, did). But life in Paris was not comfortable. It was boring, bleak, and lonely. Many people shunned Picasso as a shirker. His studio looked out over the Montparnasse cemetery, where only the spooky monument to Baudelaire offered him relief from the rampant nationalism of the time.

By that summer day, Picasso was desperate for a break and searching for a new community to support his art. Cocteau was eager to spice his comfortable bourgeois existence with the excitement of bohemia. For a few years, they became a team. The courtship began early in the summer of 1916, and by August it was in full swing. Thus Cocteau's decision to bring the camera and focus nearly every shot on Picasso. In those days, Jean was "the media."

Among those depicted, only Jacob and Salmon were part of the intellectual circle that had created and nurtured Cubism. Most of the others were new friends - Modigliani and Kisling were enjoying the chance to be seen with Picasso, Roche had contacts with wealthy collectors that might someday pay off, the model Paquerette was helping Picasso forget about Eva's death, and Ortiz, an old friend, was a wealthy Spaniard who was usually generous enough to pick up the check. But the real show was Picasso and Cocteau. Only twelve days later, Cocteau announced that Picasso had agreed to collaborate on a new ballet for Diaghilev, Parade, with music by Erik Satie. It took them to Rome in February 1917, premiered in Paris that May, and played a large role in making Picasso the phenomenon he became between the two world wars.

Most of Kluver's book first appeared as an article in Art in America. In this revised form, it demonstrates that long days spent in the archive, poring over maps and testing facts, can deliver a fascinating story and fill important holes in our knowledge of even these much-studied periods of art history. Given this approach, its narrow focus is a benefit to the educated reader.

Michael FitzGerald is chairman of the department of fine arts at Trinity College, and the author of Making Modernism: Picasso and the Creation of the Market for Twentieth-Century Art.