In A Book of Secrets Michael Holroyd takes what might be described as the scenic route, all interesting diversions and fine views. More specifically, he takes the white-knuckle ride that links Naples to Ravello in a series of crazy hairpin bends. At the end of his trail lies the Villa Cimbrone, a fairytale castle of arched windows and bell towers, which turns out to be both the site and the subject of his latest (and, he swears, his last) biographical investigation into the lives of the not-terribly-rich and only-slightly-famous of the early 20th century.

Holroyd's intention in this shimmering book, as dreamy and heat-hazed as Cimbrone itself, is to untangle the stories of three women who passed at different times through its rustling orange groves and sun-soaked courtyards. All three initially appear to be sturdily rooted in the British establishment, and arrive trailing ball gowns, impeccable vowels and a polished sense of their own importance. Yet, it soon becomes apparent, all three have in different ways become detached from the patriarchy that underpins the bohemian fantasy that is Villa Cimbrone. The solution to their insubstantiality appears to involve tracking down the lost fathers and lovers whose shades continue to shimmer above the villa's honey-coloured walls.

The first of these women is Eve Fairfax, the fiancée of the second Lord Grimthorpe. In 1904 Grimthorpe bought Cimbrone and turned it into a dreamscape so entrancing that Lytton Strachey immediately started making plans to transplant the entire Bloomsbury community to southern Italy. As part of his courtship of Fairfax, Grimthorpe commissioned a bronze bust from Rodin but then decided he couldn't afford to pay for it. The fact that he'd grown tired of Eve and married someone else probably figured, too. The bust ended up in the V&A, where its mysterious melancholy first snagged the attention of a young Holroyd in the late 1960s.

Abandoned by Grimthorpe, Fairfax never married and spent the rest of her unfeasibly long life descending on various chilly English manor houses she had known in her youth. Holroyd is never funnier than when he is on his home territory of shabby gentility, describing the redoutable Miss Fairfax being handed gingerly from one frazzled hostess to another like a battered parcel. Her only link to her more substantial past was the autograph book which went with her everywhere. On its fraying pages you would find the signatures, sometimes accompanied by game little stabs at verse, of everyone she had ever menaced for a contribution during those long, long country house weekends. It is this book of sketchy memories and fleeting presences which Holroyd takes as the working model for his own Book of Secrets. For it is not his intention here to write the kind of monumental cradle-to-grave narratives that occupied him so magnificently from the 1960s to the 1990s. Instead he is after an effect akin to the fading chatter of people whose conversations can just about be heard from several rooms away.

His second subject is Catherine Till, an elderly gentlewoman who has good reason to believe that her real father is Grimthorpe's only son, Ralph. She hopes to find proof at Villa Cimbrone. Holroyd accompanied Till on her quest in 2000, which gives him the chance to produce one of his brilliant comic set-pieces. He watches helplessly as she wrangles in Italian for her hire-car. He attempts to palliate her crazy driving by turning his yelps of terror into stirring tally hos. He even, gallantly, tries to formulate an answer to her cheery inquiry as to whether he would rather die by driving off the mountainside or by being crushed against the rockface by an oncoming lorry.

She doesn't find exactly what she is looking for at Villa Cimbrone, but that really is the point. The villa, and Holroyd's book, comprise a kind of endless hall of mirrors in which the seeker is thrown back on her own desires. Since the 1960s the Villa Cimbrone has belonged not to Lord Grimthorpe's heirs but to an Italian family who turn out to be curiously attached to the English letters and diaries that have been left behind. In fact, so pleased are they with the patina of high-class mystery that these documents impart, that they are not at all sure they want to allow the Grimthorpe archive return to its rightful home in the Yorkshire dales. Holroyd's job, as Till's expert advocate, is to delicately bully his charming hosts into releasing their mouldy treasure. The resulting negotiations are as vaporous and inscrutable as a Japanese tea-drinking ceremony.

The final life caught up in the Villa Cimbrone is that of Violet Trefusis, a woman who tends to be remembered these days for her indiscreet love affair with Vita Sackville-West rather than for the sharp, smart novels she wrote in the middle decades of the 20th century. As she was the daughter of Alice Keppel, Edward VII's "La Favorita", there has always been a rumour that Violet was actually fathered by the king. In fact the timing is off and the more likely candidate for that honour is her younger sister Sonia, grandmother to the Duchess of Cornwall. More likely altogether is that Violet was the illegitimate daughter of the priapic Lord Grimthorpe, with whom Keppell dallied on her way to a bigger bed. This thread of disputed DNA is what links the late-Victorian aesthete Grimthorpe to a later generation of Bloomsberries and explains how Strachey, Woolf, Keynes and Forster came to fall under Cimbrone's spell.

If this sounds complicated, then that's because it's supposed to. Holroyd's main point is to create one of those states that exist in dreams where fathers, lovers, brothers and mothers merge into one another and time and place collide. Villa Cimbrone, it turns out, offers very few answers to his three heroine's various lacks. In fact it stubbornly resists the part which grand houses tend to play in stories such as these, where a drawer is pulled out to reveal the hidden letter that will explain everything. Indeterminacy is what Holroyd is after here. And just as his earlier biographies captured the desire to read about lost lives in all their teeming detail, so in his Book of Secrets he has once again caught the present moment, what we might call the post-biographical mood, perfectly.

Kathryn Hughes's The Short Life and Long Times of Mrs Beeton is published by HarperPerennial.

Early in this gem of a book, Michael Holroyd points out that it marks the last volume in his "confessions of an elusive biographer", a trilogy that began with his memoir Basil Street Blues and then, in Mosaic, moved sideways to explore two enigmatic women interlaced in the family tapestry.

Here, the links with earlier volumes are all thematic and the elusiveness is hardly the biographer's alone. Life itself, this consummate writer of lives shows us, is slippery and mysterious. The atmosphere of this meditation on life and the attempt to capture it in writing is as dreamlike as the place which ties its various elements together: the magical Villa Cimbrone perched high above Ravello and the Gulf of Salerno, where Lytton Strachey, one of Holroyd's earlier subjects, had a fantasy of replanting Bloomsbury. Holroyd came here at different times with both of the present book's dedicatees, who appear in its pages as fellow searchers after ever-elusive truths.

One seeks confirmation of the hope that the father she wishes for was in fact hers and the son of the second Lord Grimthorpe, the late Victorian banker, art lover, politician and philanderer who had bought and rebuilt the villa in the early 1900s. His ashes lie beneath the stone floor of its temple. His vagrant seed and abandoned loves populate the book's stories.

Holroyd's other dedicatee is an Italian biographer, something of a foil for Holroyd himself. She came to the Villa Cimbrone in search of the spirit of her beloved novelist, Violet Trefusis, who had lived in the house with her mother, Alice Keppel, mistress of the Prince of Wales. Here, Vita Sackville-West had visited the young Violet before the Great War and lived out a chapter in the passionate love affair which fed both their fictions as well as Virginia Woolf's Orlando. Lavish and excessive, Violet was, in fact, Grimthorpe's illegitimate daughter.

But the woman with whose story this "book of secrets" begins is Eve Fairfax, the sometime muse of Auguste Rodin. It was while he was a young researcher at the Victoria and Albert Museum that Holroyd developed a fascination for the bronze bust Rodin had made of Eve. Its lingering air of melancholy haunted. He started to make inquiries.

Eve Fairfax, it transpires, was the fiancee of the second Lord Grimthorpe. It was he who commissioned her bust from Rodin in 1901 and sent her to Paris, complete with chaperone, for sittings. In the event, Eve's amorous friendship with Rodin long outlasted her engagement to Grimthorpe. She sat for Rodin over some eight years. They met in Paris or in London and she became for him a femme inspiratrice, the model for some of his best late work.

He paid her the greatest of compliments: "I regard you as a woman who resembles in expression as well as in form one of the 'faces' of Michelangelo." Grimthorpe, having suddenly abandoned Eve in 1904, never paid for the original commissioned bust.

Left impoverished and single, though with an illegitimate son Holroyd has retrieved from scraps of evidence, Eve lived out her life as something of an aristocratic nomad, moving from one grand house to another, until she died at the ripe age of 107 in 1978. Had he but known, Holroyd could have met her. Instead, he is left to conjure her life from her own thick book of secrets  a burgeoning tome she carried from house to house and in which those she met were asked to write.

Alice Keppel appears here. So, too, does Eve's one-time fiance, Grimthorpe, met again in 1915, two years before his death. He leaves Eve a verse from Swinburne's "Dolores", chilling in its resonance. Its last lines read: "And marriage and death and division/Makes barren our lives"

Reading this book is a little like walking through a hall of mirrors into the final party of Proust's great opus. The rouged and powerful dowagers loom largest: the ancient Eve Fairfax herself; the corpulent Lady Sackville, who also sat for Rodin; Alice Keppel, barred from royal circles once her Prince of Wales was dead, but ever-idolised by her wild daughter; Violet's older and sadistic lover/mother, the Princess Edmond de Polignac; Violet herself, as she takes on years, rouge, and books. Their children have little idea that these women were once aspiring and amorous coquettes whose adventures subtly echo through their heir's lives and in turn down through subsequent generations.

The terrain where aristocracy and bohemia mingle is one of which Holroyd is a past master. Here, he has given us the distilled essence of biography and a fitting end to what he evokes as the "comedy of life".

Lisa Appignanesi's Mad, Bad and Sad: A History of Women and the Mind Doctors from 1800 to the Present is published by Virago.