The Beautiful Fall: Fashion, genius and glorious excess in 1970s Paris by Alicia Drake

In the long morning before the postman delivered Drake's book, I read Cathy Horyn in The New York Times on the end of the affair with designers. She's the quietest fashion critic, never a shriek emitted, and her CV for such unemployed talent as Tom Ford and Jil Sander was the proper preface to this twinned biography of Yves Saint Laurent and Karl Lagerfeld, Sun King and perpetual Regent of a regime that now seems ancien.

Drake places the foundation of their reign at a date distant from the usual collections cited; in August 1970, when KL's earnings sponsored the Saint Tropez vacation of four young Americans: the illustrator Antonio Lopez, who had aspired his way out of Puerto Rican poverty; his ex-lover/collaborator; a naughty boy acting as stylist; and a model. All had hung out in New York with Andy Warhol's Factory hands, and their techniques of image construction were different from clothes-based Euro-couture. The men and their made-over girl merged "street, screen, art, irony, music and the individual", referring to these, and the past, only to source costume or pose for their masquerades. Their purpose was to be seen to be, then to be sketched or Polaroided, with the resultant images added to their collaged references, their mood board, available for further synthesis. KL (aged 36 by Drake's chronology, aeons less by his own) watched. KL amended his strategy.

It's a perceptive scene, the moment when Warholian glamour - a pictured illusion, only moderate stitchery necessary - intersected with fashion and then dominated it for over three decades. By 1970, YSL and KL were both establishment, albeit in different milieus. YSL had come out of middle-class Oran in colonial Algeria, and been apprenticed in Paris before the end of the previous dynasty of grand couturiers whose cloth sculptures enwrapped a few wealthy wives. He was fearful of duchesses and mindful of models working a pocket as they paraded through the salon in silence, not elevated above the clients in that pre-catwalk era; when he found his mode in his own house, it stayed predicated on old-style style. He was obsessive, reclusive, and powerfully dependent on his spiritual spouse and business manager, Pierre Bergé. KL, from middle-class Bad Bramstedt in Germany (Drake has found out the number of bedrooms in the family house - four - proving it more manse than the mansion of KL reminiscences), made handsome sums as an anonymous, prolific supplier of designs to high-grade ready-to-wear businesses. He was obsessive, promiscuously social, and independent, since he was his own titanium-brained money manager. KL and YSL had been friends when fresh in Paris, but YSL then palisaded himself behind a permanent court, while KL gadded everywhere.

The competitive cliques were interlinked soon after the St Tro' summer of self-love, by a third provincial fantasist, Jacques de Bascher, who made a determined entry into their leaders' lives. JdeB is the revelation of Drake's narrative, a far more modern figure than his admirers KL and YSL. He had come from Saigon via the dire middle-classness of suburban Neuilly, although his relations did also inhabit a pauvre château of sorts. Judged by the standards of YSL and KL, JdeB was sans talent. He couldn't create anything that could be sold: no YSL shoulder as shrugged by Catherine Deneuve, no rails of Chloe prêt-a-porter as snapped up by women across Europe. His inventions were party invites, black mischief and a persona as an elegant aristo, vestigially moustached, with his undervests buttoned to his underpants. KL's Warholian equipage had seldom confused who they were with what they projected Instamatically, but JdeB tried to become what he wanted to be through being seen as such. His mad, bad behaviour in the 1970s (Drake tots up seven days a weary week of miserable pleasure-seeking) predicts reality telly, albeit at a superior level of drug and other consumption. KL long-term subsidised JdeB to do his living for him, or anyway the risky bits. YSL's temporary but intense fixation on JdeB ended the YSL-Bergé marriage and propelled YSL into drink, drugs and some magnificent, though scarcely reality-based, collections.

JdeB died of Aids in 1989, a sombre definition of fashion victimhood. His devotees, though fabulously successful, went on leading grim lives: perpetual pursuit of perfection through appearances is a terrible sentence. YSL has become chief exhibit (seldom on show) in the museum of his creative past, erected and curated by Bergé; KL continues to do his best work as a pasticheur, re-channelling Chanel. His slimmed, rejuvenated marionette self now signifies more than all the knowledge and effort of his half a century of invention.

That I ended feeling triste about them all, rather than longing to load a tumbril with the guests at Loulou de la Falaise's wedding and the names on the interview list at the back of the book, is a tribute to Drake. Her research is persistant and patient; it must have been exasperating to establish A Single Fact in a monde of floss, spat, spin and lie. Her reconstruction of the suicide of JdeB's loser ami, Jose de Sarasola, is discreet; for KL and his muse, Anna Piaggi, it was business as usual at Karl'schâteau. (JdeB explained decadence as "the beautiful way to fall".) Drake's aperçus are apt, too: YSL's perfume Opium does invoke cocaine, not poppy narcotic. Most surprising, she is kind to her preposterous cast: their sins are analysed, then accepted in charity. Nobody's perfect, not even Marie-Hélène de Rothschild gowned by YSL for a Proustian ball: she demanded that the sleeves be cut off. All in the past, of course, now that - as Horyn reports - Proctor & Gamble is corporate parent to a couture house and "fashion faces the challenge of how to be meaningful". Meaningful?