She dialled Ronnie’s mobile number and once more got the lines-busy beep.

She tried again. Again. Again. Her heart was thrashing around inside her chest and she was shaking, desperate to hear his voice, to know that he was OK. And all the time inside her head was the knowledge that Ronnie’s meeting was in the South Tower. The South Tower had collapsed.

She wanted more pictures of Manhattan, not the sodding Pentagon, Ronnie was in Manhattan, not the sodding Pentagon. She changed channels to Sky News. Saw another jerky hand-held shot, this time of three dusty firemen in helmets carrying a busted-looking grey-haired man, their yellow armbands jigging as they walked urgently along.

Then she saw a burning car. And a burning ambulance. Figures appearing out of the gloom behind them. Ronnie? She leaned forward, close up to the huge screen. Ronnie? The figures appeared from the smoke like faces on a developing photograph. No Ronnie.

Then she dialled his number again. For one fleeting moment it sounded as if it was going to ring! Then she was thwarted by the lines-busy signal once more.

Sky News cut to Washington. She grabbed the remote and hit another button. It seemed that every station was now showing the same images, the same news feeds. She watched a replay of the first plane striking, then the second. It replayed again. And again.

Her phone rang. She hit the answer button with a sudden burst of joy, almost too choked to get any words out. ‘Hello?’

It was the washing-machine engineer, calling to confirm his appointment for tomorrow.

The target’s name was Ricky. Abby had met him on a few occasions at parties, when he always seemed to make a beeline for her and chat her up. And in truth, she found him attractive and enjoyed the flirtation.

He was a good-looking guy in his forties, slightly mysterious and very self-assured, with the air of an ageing laid-back surfer dude. Like Dave, he knew how to talk to women, asking her more questions than he answered for her. He was also involved in stamps, in quite a big way.

Not all the stamps were his own. Four million pounds’ worth, to be precise. There was some dispute over their ownership. Dave told her that he and Ricky had made a deal to split the proceeds fifty-fifty, but now Ricky was reneging and wanted ninety per cent. When she had asked Dave why he didn’t simply go to the police he had smiled. Police, it seemed, were off limits for both of them.

Anyhow, he had a much better plan.

Roy Grace was still struggling, even with the help of the direct beam of a halogen light, to see the minute object Frazer Theobald was holding up in his stainless-steel tweezers. All he could make out was something blue and blurred.

He squinted, reluctant to admit to himself that he was getting to the point where he needed glasses. It was only when the pathologist placed a small square of paper behind the tweezers and handed him a magnifying glass that Roy could see it more clearly. It was a fibre of some kind, thinner than a human hair, like a gossamer strand of a spider’s web. It appeared translucent one moment, then pale blue the next, and the ends were jigging from a combination of the faintest tremor in Theobald’s hand and the icy breeze blowing through the storm drain.

‘Whoever killed this woman did his best to leave no evidence,’ the pathologist said. ‘It’s my guess he put her down here expecting that at some point she’d be washed along through the drainage system and then flushed out of the sewage outfall into the sea – thinking a sufficient distance from the shore for sewage would be a safe enough distance for a body.’

Grace stared again at the skeleton, unable to get the possibility that it was Sandy out of his mind.

‘Perhaps her killer hadn’t considered the drain not flooding,’ Theobald went on. ‘He hadn’t reckoned on her getting embedded in the silt, and because the water table was down, there wasn’t enough flow through the drain system to wash her free. Or maybe the drain went out of use.’

Grace nodded, looking again at the twitching thread.

‘It’s a carpet fibre, that’s what I think. I could be wrong, but

I think the lab analysis will show it’s a carpet fibre. Too hard to be from a pullover or a skirt or a cushion cover. It’s a carpet fibre.’

Joan Major nodded in agreement.

‘Where did you find it?’ Grace asked.

The forensic pathologist pointed at the skeleton’s right hand, which was partially buried in the silt. The fingers were exposed. He pointed at the end of the middle finger. ‘See that? It’s an artificial nail – from one of those nail studio places.’

Grace felt a chill run through him. Sandy had bitten her nails. When they were watching television she would chew on them, making busy little clicking sounds like a hamster. It drove him nuts. And sometimes in bed as well. Often when he was trying to go to sleep, she would be gnawing away, as if fretting about something she could not or would not share with him. Then suddenly she’d look at her nails and get angry with herself, say to him that he must tell her when she was biting and help her to stop. And she would go to a nail studio to have expensive, artificial nails put over her bitten ones.

‘A plastic compound, glued on, somehow the nails didn’t get washed away when the skin beneath rotted,’ Frazer Theobald said. ‘The fibre was beneath this one. It could be that her assailant dragged her along a carpet and she dug her nails in. That’s the most likely explanation of how it got there. Bit of luck that it didn’t get washed away.’

‘Luck, yes,’ Grace said distantly. His mind was racing. Dragged along a carpet. A blue carpet fibre. Pale blue. Sky blue.

There was a pale blue carpet at home. In the bedroom. The bedroom he and Sandy had shared until the night she disappeared.

Into the blue.

Ronnie had been running for maybe a minute when day changed into night, as if there had been an instant, total eclipse of the sun. Suddenly he was stumbling through a choking, stinking void, with the sound of thunder in his ears, thunder that was rising from the ground.

It was as if someone had emptied a billion tons of foul-smelling, bitter-tasting black and grey flour into the sky directly above him. It stung his eyes, filled his mouth. He swallowed some of it and coughed it back up, immediately swallowing more. Grey shapes like ghosts swirled past him. He stubbed his toe painfully on something – a fire hydrant, he realized – as he tripped over the damned thing and fell forward, hard, on to the ground. Ground that was moving. It was vibrating, quaking, as if some giant monster had awakened and was breaking free from the belly of the earth itself.

Have to get out of here. Away from here.

Someone trod on his leg and crashed down on top of him. He heard a woman’s voice, cursing and apologizing, and smelled a fleeting whiff of fine perfume. He wriggled free of her, tried to stand up, and immediately someone slammed into his back, hurtling him forward again.

Hyperventilating in panic, he scrambled to his feet and saw the woman, looking like a grey snowman clutching a pair of court shoes, get up. Then a huge fat man with mad hair crashed into him, cursing, punching him out of the way, and ran stumbling on to be swallowed by the fog.

Then he was knocked over again. Got to get up. Get up. Get up!