Theo and David Holroyd had set up in partnership not long after Theo's marriage to Valerie. Jean Stanton joined them a couple years later. All three of them had been at university together and they wanted a "go-ahead, socially responsible" law practice, the kind that did more than its fair share of domestic and matrimonial and legal-aid work. Their good intentions had weakened over the years. Jean Stanton had discovered she liked litigation more than domestic violence and that her politics had changed from center left to Conservative with a large "C," and David Holroyd found that, as a fifth-generation East Anglian lawyer, conveyancing was his lifeblood, and so it usually fell to Theo to "keep up the ethical end of it," as David Holroyd put it. The practice had grown substantially, there were three junior partners now and two associates and they were bursting at the seams in the Parkside office, but none of them could bear the idea of moving.

The building had been a dwelling-house originally, five floors in all, from damp kitchen cellar to servants' cold attics, the rooms piled together rather haphazardly but nonetheless a decent residence for a well-to-do family. After the war it had been broken up into businesses and flats and now only fragmented and ghostly traces of the interior remained – a decorative plasterwork border of swags and urns above the desk where Cheryl worked and the egg-and-dart frieze beneath the cornice in the hall.

The drawing room, oval ended and neoclassic in its restraint, with a view of Parker's Piece from the windows, was now the boardroom for Holroyd, Wyre, and Stanton, and in winter there was always a real coal fire burning in the grate of the marble fireplace because David Holroyd was an old-fashioned sort. Theo had stood in the boardroom many times, sharing a glass of wine with his partners and associates, all of them full of the provincial bonhomie of successful professionals. And, of course, Jennifer and Laura had been in and out of that place all the time, ever since they were little, but it was still odd to think of her in there today, filing and fetching and carrying, and he knew how polite and willing she would be and felt proud because everyone in the office would be saying to one another, "Laura's a lovely girl, isn't she?" the way that people always did.

Sheep on the line. The ticket inspector did not elucidate whether it was a flock or a few stragglers. Enough of them anyway for everyone on the train to Cambridge to feel the bump and judder. The train had been stopped for ten minutes before the conductor made his way through the four carriages and informed them about the sheep, quashing speculation about cows, horses, and suicidal humans. After half an hour the train was still stationary, so Theo supposed it must be a flock rather than some solitary stray. He wanted to get back to Cambridge and take Laura out for lunch but it was "in the lap of the gods," as the conductor put it. Theo wondered why it was the lap of the gods and not the hands of the gods. It was stifling in the train, and someone, the guard presumably, opened the doors and people began to clamber out. Theo was sure it was against railway bylaws, but there was a narrow verge and an embankment at the side of the train so it seemed quite safe, there was no way another train could plow into them in the way that theirs had into the sheep. Theo alighted cautiously, and with difficulty, pleased with himself for being so adventurous. He was curious to see what sheep looked like after a close encounter with a train. Walking along the track, he soon discovered the answer to his question – bits of sheep, like joints of meat with wool attached, had been flung about everywhere, as if they'd been torn apart in a bloody massacre by a pack of wolves. Theo was surprised how strong his stomach was for this carnage, but then he had always regarded lawyers as being rather like policemen and nurses in their ability to rise above the mess and tragedy of everyday life and deal with it in a disinterested way. Theo had a strange sense of triumph. He had traveled on a train that had almost been derailed but no harm had come. The odds surely dictated that his chances (and therefore the chances of those close to him) of being in another train accident had lessened.

The driver was standing next to his engine, looking baffled, and Theo asked him if he was "okay," and he said, by way of answer, "I saw just the one and I thought, Well, I probably don't need to brake for that, and then" – he made a dramatic gesture with his arms as if trying to reenact a flock of disintegrating sheep – "and then the world went white."

Theo was so taken by this image that it occupied his mind for the rest of the journey, which recommenced once they had transferred to another train. He imagined describing the scene to Laura, imagined her reaction – horrified and yet darkly amused. When he finally got off the train he took a cab halfway but then got out and walked. It would make him even later but Laura would be pleased.

Theo rested for a minute on the pavement before tackling the steep stairs up to the first-floor office of Holroyd, Wyre, and Stan-ton. The GP was right, Laura was right, he had to lose some weight.

The front door was propped open with a cast-iron doorstop. Every time Theo entered the building he admired this door to the office, it was painted a glossy dark green, and the handsome brass furniture – letter box, keyhole, lion-headed door knocker – were the original fittings. The brass plaque on the door, polished every morning by the office cleaner, announced, HOLROYD, WYRE, AND STANTON-SOLICITORS AND ATTORNEYS-AT-LAW. Theo took a deep breath and set off up the stairs.

The inner door that led into the reception area was also – unusually – open, and as soon as Theo walked in it was obvious that something was terribly wrong. Jean Stanton's secretary was cowering on the floor, a trail of vomit on her clothes. The receptionist, Moira, was on the phone, dictating the address of the firm with a kind of hysterical patience. She had blood in her hair and on her face and Theo thought she was injured but 'when he went toward her to help her she waved him away with her hand and he thought she was dismissing him until he realized she was trying to send him in the direction of the boardroom.

Afterward, again and again, Theo pieced together the events that preceded this moment.

Laura had just finished photocopying a land registry form when a man came into reception, a man so nondescript that afterward not one single person in Holroyd, Wyre, and Stanton could give a half-decent description of his features, and the only thing they could remember about him was that he was wearing a yellow golfing sweater.

The man seemed confused and disoriented, and when Moira, the receptionist, said, "Can I help you, sir?" he said, "Mr. Wyre, where is he?" in a high, strained voice, and Moira, alarmed by the man's manner, said, "I'm afraid he's late back from court, do you have an appointment? Can I help with anything?" but the man took off down the corridor, running in an odd way, like a child, and charged into the boardroom where the partners were having a lunchtime meeting, although not Theo, who was still on his way back from the station (although he had forgotten about the meeting).

Laura had been sent out earlier to buy sandwiches for the meeting – prawn cocktail, cheese and coleslaw, roast beef, tuna and sweet corn, and a chicken and salad (no mayonnaise) for her father because he really needed to think more about his weight and she had thought affectionately what a dope he was because he'd forgotten his meeting when he'd suggested lunch to her this morning. The sandwiches and coffee and notebooks were all laid out on the mahogany boardroom table (oval to match the shape of the room) but no one had sat down at the table yet. David Holroyd was standing in front of the fireplace, telling one of the junior partners about the "bloody fantastic" holiday he'd just returned from, when the stranger rushed into the room and from somewhere, probably from beneath the yellow golfing sweater he was wearing, but no one was sure, pulled out a bowie knife and sliced through the dark worsted of David Holroyd's Austin Reed suit, the white poplin of his Charles Tyrwhitt shirt, the tropical tan on the skin of his left arm, and, finally, the artery in the arm. And Laura, who liked apricot yogurt and drank tea but not coffee and who had size six feet and who loved horses, who preferred plain chocolate to milk chocolate and had spent five years learning classical guitar but never played anymore and who was still sad that their pet dog, Poppy, had been run over the previous summer, Laura, who was Theo's child and his best friend, dropped the land registry form and ran into the boardroom after the man – perhaps because she had a Red Cross certificate or because she had taken a self-defense course at sixth-form college, or perhaps it was from simple curiosity or instinct, it was impossible to know what she was thinking as she ran into the boardroom where the man, this complete stranger, had spun on the balls of his feet with the agility and grace of a dancer, his hand still moving in the same arc that had cut through David Holroyd's arm and which now scythed through Laura's neck, carving through her carotid artery, sending a great plume of her precious, beautiful blood across the room.