Soon, too soon, she taught herself to read and vanished for long hours into her attic with a book, to be discovered by one of the servants shivering with a cold she had been too absorbed to notice. If she spoke now, it was to her invisible playmate — a twin brother, fleet-footed and strong — or to the small creatures she befriended in that loveless house: the sparrows which settled on her window-sill; a squirrel she had called down from the one tree in the raked gravel rectangle which was the Mortons’ garden.

Yet it would be wrong to say that Harriet was neglected. If Louisa found it impossible to love this child of the frivolous usurper who had ensnared her brother, she was determined to do her duty. Harriet was conveyed to music lessons and to dancing classes which the family doctor, disconcerted by her pallor and thinness, recommended. She was regularly aired and exercised, sent on long walks with whatever ancient and grim-faced maid survived Louisa’s regime. If her father grew crustier and more bigoted as the years passed, he could still recognise academic excellence and himself taught her Latin and Greek.

And presently she was sent to an excellent day school most highly recommended by the ladies of the Trumpington Tea Circle who ruled Louisa Morton’s life.

No child ever loved school as much as Harriet. She was ready to leave with her satchel an hour before it was time to go; she begged for any job, however menial, which would keep her there in the afternoon. Arithmetic lessons, sago pudding, deportment… she enjoyed everything because it was shared by others and accompanied by laughter — because there was warmth.

Then a new headmistress came, detected in the vulnerable dark-eyed child a potential scholar, and herself coached her in English and History: lessons that Harriet was to remember all her life. After two terms she sent for Professor Morton in order to discuss Harriet’s university career. Did he favour Newnham or Girton, she enquired, pouring tea for him in her charming sitting-room — or would it be sensible to choose an Oxford college so as to give Harriet a fresh environment? Though it was always foolish to prophesy, she would be extremely surprised if Harriet failed to get a scholarship…

From the interview which followed both parties were invalided out in a state of fulminating rage. To the Professor it was genuinely incomprehensible that anybody could have lived in Cambridge for one week and not known his views on ‘women in the university’. And, unable to trust his daughter to this suffragette upstart, he took Harriet away from school.

That had been a year ago and Harriet could still not pass the familiar red brick building without a lump in her throat.

Now she threw her last crust of bread, narrowly missing the head of the Provost of St Anne’s who appeared suddenly in a punt beneath her, poling his blonde wife and pretty daughters down-river. To have hit the Provost would have been a particular disaster, for he was her father’s enemy, having criticised Professor Morton’s entry on Ammanius Marcellinus in the Classical Dictionary, and his wife — whose friendly wave Harriet could not help returning — was even worse, for she had been found (while still Secretary of the Association of University Wives) unashamedly reading a book by someone dirty called Sigmund Freud while in a hansom parked outside Peterhouse.

‘Poor child!’ said the Provost when they were out of earshot.

‘Yes, indeed,’ agreed his wife grimly, looking back at the forlorn little figure on the bridge. ‘How such a charming, sensitive child came to be born into that household of bigoted prigs, I shall never understand. It was a crime to take her away from school. I suppose they regard it as a perfectly fitting life for her — arranging flowers in a house where there are no flowers, taking the dog out when there isn’t any dog.’

‘There is a young man, one hears,’ murmured the Provost, expertly shooting beneath Clare Bridge, and raised his eyebrows at his wife’s most unladylike snort.

The Provost was correct: there was a young man. His name was Edward Finch-Dutton; he was a Fellow of the Professor’s own College, St Philip’s, and though his subject was Zoology — a new and upstart discipline of which it was impossible to approve — the Mortons had permitted him to come to the house. For there had been ‘unpleasantness’ about the decision to keep Harriet at home. Even the Master of Trinity, who ranked slightly below God, had taken the Professor aside after the University sermon to express surprise.

‘After all, you have made quite a little scholar of her yourself,’ he said. ‘I had a most enjoyable chat with her the other day. She has some highly original views on Heliodoras — and a delightful accent.’

‘If I taught Harriet the classics, it was so that she could make herself useful to me at home, not so that she could become an unfeminine hoyden and a disgrace to her sex,’ the Professor had replied.

Still, the encounter had rankled. Fortunately, in her dealings with her niece, Louisa had one unfailing source of guidance: the ladies of the Trumpington Tea Circle who had seceded from the Association of University Wives when it became clear that the parent body could no longer be relied upon to uphold etiquette and protocol. It was these ladies — headed by Mrs Belper, Louisa’s special friend — who had suggested that the best solution for Harriet might be an early marriage. Seeing the sense of this, the Mortons, rejecting various men who had shown an interest in Harriet (for unaccountably the child seemed to have the gift of pleasing) had selected Edward Finch-Dutton. He had a First, was sensible and ambitious and was related — albeit distantly — to the Master of St Swithin’s, Oxford. Not only that, but his mother — a Featherstonehaugh — had been accustomed to visit Stavely, the district’s most beautiful and prestigious home.

It was the long, serious face of this excellent young man that Harriet saw now as she looked into the water; and as always, his image brought a stab of fear.

‘Don’t let me give in, God,’ she begged, tilting back her head, sending the long soft hair cascading down her back as she searched the quiet, dove-grey sky of Cambridge for some portent — Halley’s comet; the pointing finger of Isfrael — to indicate deliverance. ‘Don’t let me marry Edward just to get away from home. Don’t let me, God, I beg of you! Show me some other way to live.’

A church clock struck four, and another… and suddenly she smiled, the grave little face utterly transformed as she picked up her case. Somehow her dancing lessons had survived; those most precious times were left to her. And abandoning the resolutely silent firmament, she quickly made her way beside the verdant lawns towards King’s Parade.

Ten minutes later she entered the tall, shabby building in Fitzwilliam Street which housed the Sonia Lavarre Academy of Dance.

At once she was in a different world. The streets of Cambridge with their bicycles and dons might never have existed and she could be in St Petersburg in the Tsar’s Imperial Ballet School in Theatre Street, where Madame Lavarre — then Sonia Zugorsky — had spent eight years of her childhood. A tiled stove, incorrectly installed by a baffled Cambridge plumber, roared in the hallway; the sad Byzantine face of St Demetrius of Rostov stared at her from the icon corner…

And everywhere, covering the panelled walls, climbing up the stairway, were daguerrotypes and paintings and photographs… of Kchessinskaya, erstwhile mistress of the Tsar, en pointe in Esmerelda… of the graduation class of 1882 with Madame in a white dress and fichu, demure and doe-eyed in the front row… of rose-wreathed Taglioni, the first Sylphide of them all, whose ballet slippers had been cooked and eaten by her besotted Russian admirers when she retired.

For it was not genteel ballroom dancing which was taught by Madame — beached-up in Cambridge after a brief marriage to a French lecturer who died — but the painful and manically disciplined art of the ballet.

Harriet hurried upstairs, smiling as she passed the open door of Room 3 from which came the sounds of a Schubert impromptu, its rhythm relentlessly stressed to serve the wobbly pliés of the beginners with their gap-teeth and perilously slithering chignons. ‘My Pavlova class,’ Madame called it, blessing the great ballerina whom she knew and cordially disliked. For these were the children of mothers who on some shopping trip to London had seen Pavlova in Giselle or The Dying Swan and had come to believe that perhaps ballet was not just something done by girls who were no better than they should be.

There were only four pupils in the advanced class with Harriet and all of them were there before her in the changing-room. At first they had been aloof and unfriendly, rejecting Harriet with her snobbish university background. Phyllis — the pretty one, with her blonde curls — was the daughter of a shopkeeper; she had added ballet to ‘stage’ and already danced in pantomime. Mabel, conscientious and hardworking and inexorably fat, was the daughter of a railway clerk. Red-haired Lily’s mother worked in the Blue Boar. Harriet, with her ‘posh’ voice, arriving at the beginning with a maid to help her change and skewer up her hair, had been an object of derision and mockery.

But now, survivors of nine years under the whip of Madame’s tongue, they were all good friends.

‘She’s got someone with her,’ said Phyllis, tying her shoes. ‘A foreigner. Russian, I think. Funny-looking bloke!’

Harriet changed hurriedly. In her white practice dress, her long brown hair scraped back from her face and coiled high under a bandeau, she was transformed in a way which would have disconcerted the ladies of Trumpington. The neat and elegant head; the long, almost unnaturally slender throat; the delicate arms all signalled an unmistakable message — that here in this place Professor Morton’s quiet daughter was where she belonged.

The girls entered, curtseyed to Madame — formidable as always in her black pleated dress, a chiffon bandeau tied round her dyed orange hair — and took their places at the barre.

‘This is Monsieur Dubrov,’ Madame announced. ‘He will watch the class.’

She stabbed with her dreaded cane at the cowed accompanist, who began to play a phrase from Delibes. The girls straightened, lifted their heads…

‘Demi-plié… grand plié… tendu devant… pull up, everybody… dégagé… demi-plié in fourth… close.’

The relentless, repetitive work began and Harriet, emptying her mind of everything except the need to place her feet perfectly, to stretch her back to its limit, did not even realise that while she worked she was for once completely happy.

Beside the petite and formidable figure of Madame stood Dubrov, his wild grey curls circling a central dome of pinkly shining scalp, his blue eyes alert. He had seen what he wanted to see in the first three minutes; but this portly, slightly absurd man — who had never danced a step — could not resist, even here in this provincial room, tracing one perfect gesture which had its origin in Cecchetti’s class of perfection in St Petersburg or — even in the fat girl — the épaulement that was the glory of the Maryinsky. How Sonia had done it with these English amateurs he did not know, but she had done it.

‘You will work alone now,’ ordered Madame after a while. ‘The enchaînment we practised on Thursday and led her old friend downstairs. Five minutes later they were installed in her cluttered sitting-room, stirring raspberry jam into glasses of tea.

‘Well, you are quite right,’ said Dubrov. ‘It is the little brown one I want. A lyrical port de bras, nice straight knees and, as you say, the ballon… an intelligent dancer and God knows it’s rarely enough one sees a body intelligently used.’ But it was more than that, he thought, remembering the way each phrase of the music had seemed literally to pass across the child’s rapt, utterly responsive face. ‘Of course her technique is still—’

‘I’ve told you, you cannot have her,’ interrupted Madame. ‘So don’t waste my time. Her father is the Merlin Professor of Classical Studies; her aunt comes here as if there was a bad smell in the place. Harriet was not even allowed to take part in a charity performance for the police orphans. Imagine it, the orphans of policemen, is there anything more respectable than that?’ She inserted a Balkan Sobranie into a long jet holder and leaned back in her chair. ‘The child was so disappointed that I swallowed my pride and went to plead with the aunt. Mon Dieu, that house — it was like a grave! After an hour she offered me a glass of water and a biscuit — one biscuit, completely naked, with little holes in it for drainage.’