Bloomsbury Ballerina, by Judith Mackrell

'Poor little wretch, trapped in Bloomsbury," Virginia Woolf wrote of Lydia Lopokova. She pirouetted into the Group in 1921, then married Maynard Keynes: revered economist, "Higher Sodomite" and its cleverest player. Lydia, the Bloomsburyites complained, prattled in broken English, had no aesthetic style, and her manners were worse than bizarre.

Diaghilev's Ballets Russes that year staged a return London production of The Sleeping Princess. Lopokova danced the Lilac Fairy, Princess Florine and Aurora. The production flopped, Diaghilev bunked off, the cast had no money, and Keynes went nightly to the half-empty Alhambra to watch Lopokova dance. Within two weeks he was telling Vanessa Bell he was "entangled".

He opened a bank account in Lydia's name, found rooms for her a few doors from his house at 46 Gordon Square. After she divorced Diaghilev's business manager, her bigamist husband Randolpho Barocchi, he married her. Keynes was 38 and eminent. He had been chief Treasury representative at the 1919 Paris Peace Conference, written The Economic Consequences of the Peace and was an authority on post-war reconstruction. He had never had a relationship with a woman. For some years his intimate life was tied up with Lytton Strachey because they were both in love with Duncan Grant, who went on to father a child with Vanessa Bell... His current lover, Sebastian Sprott, was a Cambridge academic psychologist.

Judith Mackrell rather skates over any emotional muddle between bride and groom. She says they "fell in love", that "the war had helped transform bachelor buggers into husbands", that Lydia's "erotic ingenuity and emotional determination broke the pattern of his homosexuality". Maybe. But money, criminal law, ambition and lavender cover-up perhaps played a part. Whatever the motivation, Mackrell excels at conveying how unwanted Lydia was by Bloomsbury.

Virginia Woolf's jibes were the snidest. Lydia, she said, had the "soul of a squirrel". Clive Bell said Lydia's spiritual home was Woolworth's. At Gordon Square, where Duncan Grant and Vanessa and Clive Bell had lodged with Maynard, she painted out their murals, laid a sky-blue carpet and hung the place with fake chandeliers.

Yet the marriage seemed to work. They wrote often of their fondness for each other. Lydia's "erotic ingenuity" seemed to be blow-jobs: in early letters, she wrote of being his "licking dog". Both were driven by work as the engine for talent. Keynes spent half the week at his Cambridge college, King's, so they were apart much of the time.

To their disappointment, they had no children. He bought a lease on Tilton, a farmhouse near Charleston, his refuge in his buggery bachelor days. He continued his affair with Sebastian, though by 1925 Lydia warned she would not "serenade" him with her fingers if he continued with male lovers.

Source material on Lydia's personal life prior to Maynard is patchy. She apparently had affairs, notably with Stravinsky, she married the bigamist. She perhaps had abortions, perhaps had a child. What is successfully researched and confidently told, if rather dry to read in total, is Lopokova's impressive dancing career. Born in 1891 , she trained with the Imperial Ballet, went with Diaghilev to Paris and quickly rose to ballerina roles. Her life was demanding, dislocated and fantastical. Only Maynard gave her a home and security.

Marriage served his career. He wrote groundbreaking books; he was central to the inaugurating of the IMF and the World Bank; he financed the building of the Cambridge Arts Theatre for Lydia, but his health was poor from the 1930s on and he died in 1946 aged 63. Lydia outlived him by 35 years. After his death the Tilton farm manager, Logan Thomson, became her companion. Lydia's eccentricity turned to senility, she "began dressing like an elderly babushka", and she ended her days in the Three Ways nursing home in Seaford.

Diana Souhami's 'Coconut Chaos' is published by Phoenix