The only one who was immune to this communal clumsiness was Olivia, who in her whole three years had sustained nothing much worse than a few bruises. As for the others, their mother said she may as well have finished her nurse training, what with the amount of time she spent at the hospital.

Most thrilling of all, of course, was the day that Julia cut off her finger (Julia did seem strangely attracted to sharp objects). Julia, five years old at the time, wandered into the kitchen unnoticed by their mother, and the first Rosemary knew about the amputated finger was when she turned round from aggressively chopping carrots and noticed a shocked Julia holding her hand aloft in mute astonishment, exhibiting her wound like a martyred child saint. Rosemary threw a tea towel over the bloody hand, scooped up Julia, and ran to a neighbor, who drove them in a screech of overexcited brakes to the hospital, leaving Sylvia and Amelia with the problem of what to do with the tiny, pale finger, abandoned on the kitchen linoleum.

(An ever-resourceful Sylvia thrust the finger into a bag of frozen peas and Sylvia and Amelia caught a bus to the hospital, Sylvia clutching the defrosting peas all the way as if Julia's life depended on them.)

Their first plan for the day was to walk along the river to Grantchester. They had gone on this expedition at least twice a week since the holidays began, giving Olivia a piggyback when she grew tired. It was an adventure that took them most of the day because there were so many distractions to explore – on the riverbank, in the fields, even in other people's back gardens. Rosemary's only admonition was don't go in the river, but they invariably set off with their swimming costumes concealed under their dresses and shorts and hardly a trip went by without them stripping off and plunging into the river. They felt grateful to the afterthought for transforming their normally prudent mother into such a careless guardian. No other child of their acquaintance was enjoying such a hazardous existence that summer.

On one or two occasions Rosemary had given them money to buy afternoon tea at the Orchard Tea Rooms (where they were not the most welcome of guests), but mostly they took a hastily put together picnic that was usually eaten before they were even past Newnham. But not today, today the sun had traveled even closer to Cambridge and had them trapped in the garden. They tried to be energetic, playing a halfhearted game of hide-and-seek, but no one found a good hiding place, even Sylvia settled for nothing more creative than the nest of dry timothy grass behind the black currant bushes at the bottom of the garden – Sylvia, who had once stayed hidden and undiscovered for a record three hours (stretched like a sloth along a high, smooth branch of the beech tree in Mrs. Rain's garden opposite), only found after she fell asleep and plummeted from the tree, acquiring a greenstick fracture to her arm when she hit the ground. Their mother had a tremendous argument with Mrs. Rain, who wanted to have Sylvia arrested for trespassing (Stupid woman). They were always sneaking into Mrs. Rain's garden, stealing the sour apples from her orchard, and playing tricks on her because she was a witch and therefore deserved to be maltreated by them.

After an apathetic lunch of tuna salad they began a game of rounders, but Amelia tripped and had a nosebleed and then Sylvia and Julia had a fight that ended in Sylvia slapping Julia and after that they contented themselves with making daisy chains to plait into Olivia's hair and to collar Rascal with. Soon even this was too much effort and Julia crawled into the shade under the hydrangea bushes and fell asleep, curled up with the dog, while Sylvia took Olivia and Blue Mouse into the tent and read to them. The tent, an ancient thing that had been left in the shed by the previous owners of the house, had been pitched on the lawn since the beginning of the good weather, and they vied for space with one another inside its mildewed canvas walls, where it was even hotter and more airless than in the garden. Within minutes, Sylvia and Olivia had fallen asleep, the book forgotten.

Amelia, dreamy and languid with heat, lay on her back on the scorched grass and fired earth of the lawn, staring up at the endless, cloudless blue, pierced only by the giant hollyhocks that grew like weeds in the garden. She watched the reckless, skydiving swallows and listened to the pleasing buzz and hum of the insect world. A ladybird crawled across the freckled skin of her arm. A hot-air balloon drifted lazily overhead and she wished she could be bothered to wake Sylvia and tell her about it.

Rosemary's blood was running sluggishly in her veins. She drank a glass of tap water at the kitchen sink and looked out the window at the garden. A hot-air balloon was crossing the sky, moving like a bird caught on a thermal. Her children all seemed to be asleep. This unwonted tranquility made her feel an unexpected twinge of affection for the baby inside her. If they would all sleep all the time she wouldn't mind being their mother. Except for Olivia, she wouldn't want Olivia to sleep all the time.

When Victor proposed to her fourteen years ago, Rosemary had no idea what being the wife of a college lecturer would entail, but she had imagined it would involve wearing what her mother called "day dresses" and going to garden parties on the Backs and strolling elegantly across the plush green of the courts while people murmured, "That's the famous Victor Land's wife. He would be nothing without her, you know."

And, of course, the life of a lecturer's wife had turned out to be nothing like she had imagined. There were no garden parties on "he Backs, and there was certainly no elegant strolling across the college courts, where the grass was afforded the kind of veneration usually associated with religious artifacts. Not long after she was first married she had been invited to join Victor in the Master's garden, where it soon grew apparent that Victor's colleagues were of the opinion that he had married (horribly) beneath him ("A nurse," someone whispered, in a way that made it seem like a profession only slightly more respectable than a streetwalker). But one thing was true – Victor would be nothing without her, but he was also nothing with her. At that very moment he was toiling in the cool dark of his study, the heavy chenille curtains closed against the summer, lost in his work, work that never came to fruition, never changed the world or made his name. He was not great in his field, merely good. This gave her a certain satisfaction.

Great mathematical discoveries were made before the age of thirty, she now knew, courtesy of one of Victor's colleagues. Rosemary herself was only thirty-two. She couldn't believe how young that sounded and how old it felt.

She supposed Victor had married her because he thought she was domesticated – her mother's loaded tea tables probably misled him, but Rosemary had never made so much as a plain scone when she lived at home, and since she was a nurse he probably presumed she would be a nurturing and caring person – and she might have presumed that herself in those days, but now she didn't feel capable of nurturing a kitten, let alone four, soon to be five, children, to say nothing of a great mathematician.

Furthermore, she suspected the great work was a fake. She had seen the papers on his desk when she dusted in that hole, and his reckonings looked not dissimilar to her father's intense calculations of racing form and betting odds. Victor didn't strike her as a gambler. Her father had been a gambler, to her mother's despair. She remembered going with him to Newmarket once when she was a child. He had lifted her onto his shoulders and they had stood by the winning post. She had been terrified by the noise as the horses thundered down the homestretch and the crowd at the stand side grew frenzied, as though the world might be about to end rather than a 30/1 outsider winning by a short head. Rosemary couldn't imagine Victor anywhere as spirited as a racecourse, nor could she see him in the smoky commonalty of a betting shop.