When a woman comes along and captures the eye of an artist, we call her a muse. There were nine muses, and there were nine Garman siblings – seven sisters plus two brothers – who together set European avant-garde circles spinning in the middle of the 20th century.

Nearly all the Garmans, and certainly the four siblings – Mary, the eldest, Kathleen, Lorna, and Douglas – that writer Cressida Connolly focuses on in “The Rare and the Beautiful: The Art, Loves, and Lives of the Garman Sisters,” (Ecco, 320 pages, $25.95) were beautiful, with raven-black hair, marvelous bone structure, and intense blue eyes. They loved the arts, and artists loved them back: Vita Sackville- West, Jacob Epstein, Laurie Lee, Peggy Guggenheim, and Lucian Freud were just some of their paramours.

Little about their upbringing suggested the Garmans would become the era’s representative bohemians. Children of a well-off and generous Edwardian doctor, they were raised in a Jacobean estate in England’s West Midlands. When two of the daughters, Mary and Kathleen, were grown, they absconded to London and promptly began frequenting the haunts of the avant-garde. They lived not far from Bloomsbury, and with their exotic, gypsy looks and artistic inclinations, writes Ms. Connolly, they could have been counted among Waugh’s original Bright Young Things.

“They sought adventure, emotional altitude,” Ms. Connolly writes. Mary once claimed that she and her husband, poet Roy Campbell, were the first hippies: Peripatetic and non-monogamous, they at one point lived happily in a menage a quatre with a pair of sisters. Kathleen became the mistress of Jacob Epstein – whose wife drew a pistol and shot her in a pique of jealousy (she was injured but not seriously).

Mary later fell in love with Vita Sackville-West, who also bedded Virginia Woolf. Vita and Mary’s affair inspired “Orlando,” Woolf’s delightful pseudo-biography of a philandering, gender-bending 400-year-old aristocrat. Though the Sackville-West affair taxed Roy, he did not lose his humor: When Mary came home with cuts and bruises on her legs, he is reported to have joked, “Good Heavens, kid! I don’t mind you sleeping with Vita, but at least get her to take her earrings off!”

Out of the blessed Garman gene pool, Lorna emerged as the exemplary beauty, with searing azure eyes and auburn hair (though in photographs her highly stylized, Marlene Dietrich like eyebrows are a tad off-putting). Her peccadilloes are the most compelling. Unlike Mary, Kathleen, and the others, Lorna never faced the challenges of poverty, marrying into money at age 16. Her husband, Ernest Wishart, didn’t expect absolute fidelity, so her romantic life was thrilling.

If the other siblings’ love affairs sometimes seemed too idyllic to be convincing – free love, with its ostensible lack of jealousy, is seldom compelling as theater – Lorna’s were more complicated. Her wealth enhanced the drama; she would race to assignations in her Bentley, a sealskin coat on her shoulders and gifts filling her arms. An affair with poet Laurie Lee became so serious that Lorna left her husband – only to sulk back later, four months pregnant with Lee’s child. Wishart agreed to raise the baby as his own on the condition that Lorna stop seeing Lee. Lorna secretly continued the affair, then dropped Lee for the young artist Lucian Freud.

The fling with Freud was shorter but equally intense – Lorna inspired a number of Freud’s breakthrough paintings. When she broke off with him, inevitably, Freud went into a Heathcliffian rage, riding an enormous white horse at breakneck speed toward her sitting-room window. He later remarked, “She was a muse, a true muse in the best possible way.” (Lorna’s presence seems to have been so unforgettable that two of her lovers, Lee and Freud, settled for imitation versions of her: Both ended up marrying her nieces. This isn’t the only quasi-incestuous Garman dalliance: Mary bedded her brother Douglas’s ex-wife.)

A certain sort of biography appeals simply because it trades on our curiosity to find out who got it on with whom, and on that level Ms. Connolly’s book certainly doesn’t disappoint. She isn’t much of a social historian. But she does remind us of a few of the Garmans’ more substantial cultural contributions.

Douglas edited the “Calendar of Modern Letters,” which was funded by Wishart; it counted D.H. Lawrence, Aldous Huxley, and E.M. Forster among its contributors. Kathleen, model for a number of Epstein’s sculptures, assembled a first-rate collection of modern and post-Impressionist art – including Cezannes, Modiglianis, and Picassos. She had three children by him, and they finally married in 1955. Later she used their collection to create a new museum in the West Midlands.

Ms. Connolly doesn’t speculate on what exactly makes for a muse. Nor does she puff up the Garmans to make them more important than they really were; she exposes their flaws – especially their negligence in raising children – with as much acumen as she uses to evoke their beauty. But if the Garmans remain, finally, elusive on the page, I imagine this was true in life as well: that was what led so many lovers, and artists, to try to capture them.