The Professor’s passion for his young wife soon cooled. It was clear that Sophie would be no use to him in his career. Though constantly instructed by himself and Louisa, she seemed quite unable to learn the most basic rules of academic protocol. Again and again her patient husband caught her out in the most appalling lapses: attempting to seat the wife of the Professor of Divinity below the wife of the Professor of Mathematics and once, in a tea-shop, smiling at a young lecturer who was wearing shorts. When he was passed over for the Mastership of his College it was Sophie he blamed and Louisa — who had never really relinquished the reins of the household — now gathered them even more firmly into her bony and frugal hands.

It was into this house that Harriet was born.

Babies, as everyone who cares for them knows, come trailing their own particular essence. There are grave, contemplative babies still patently solving some equation of Euclidean geometry begun in another world, scrawny high-powered babies apparently shot into life without the slightest need to eat or sleep, and placid agricultural babies whose only concern is to thrive.

But sometimes… just sometimes, there are babies who appear to have swallowed some small private sun, rosy and endlessly obliging babies who explode into laughter long before one’s hand has actually touched their stomachs — laughter which has less to do with being tickled than with sharing and being together — and love.

Such a baby was Harriet Jane Morton in the first two years of her life: a baby who offered you her starfish of a foot, her slobbered rusk… a cornucopial life-affirmer from the start.

Then Sophie Morton, whose passion the child had been, caught a chill which turned to pneumonia, and died. Two weeks later, Louisa dismissed the country girl who had been Harriet’s nurse.

Within months the plump, rosy baby became a serious, bird-thin and almost silent little girl. As though reflecting a scarcely comprehended grief, her hair darkened, her hazel eyes lost their green and golden lights and settled to a solemn brown. It seemed as if the very skin and bone and muscle of this bewildered little being had changed into a minor key.

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.