A search of the river bank revealed no boat. Once more Marni mimed a swimming stroke. I shook my head.

We headed back into the streets. There had to be something here we could use. I walked along an alleyway, peering into back gardens and yards. Presently I heard the sound of sawing. Homing in on the sound, I came to a workshop. By lamplight a swarthy man sawed at planks of wood. Behind him stood a partially assembled wardrobe.

What caught my eye in particular were half a dozen plastic sacks filled with sawdust. I signalled to Marni to hide in the shadows.

I only had to wait a moment or so before the opportunity came. The swarthy man walked to a doorway and hollered through it. 'Joe... Joe! You ready with that coffee yet?' The carpenter listened to a distant voice. 'What's that? Joe, you said you'd be ten minutes, man. It's closer to half an hour. I got to get this furniture done for shipment or I'm not going to get my shot. There's no way I can do that if you don't keep that coffee coming. Hell, man, I'm dryer than dust out here. If you're not going to pull your weight, then I'm going to see you don't get no food. D'ya hear me, Joe?'

While the carpenter berated the unseen Joe I grabbed two sacks of sawdust. Then I returned to Marni. 'OK,' I told her. 'Let's get back to the river.'

'Just do what I do,' I said.

Marni nodded, her green gaze serious.

I emptied the plastic sack full of sawdust onto the river bank. She followed suit. Then, quickly stripping off my clothes, I stuffed them into the sack. After I'd pulled the laces out of my boots I put the boots into the sack, too.

This was no time for false modesty. Nevertheless, I made sure I looked Marni in the eye as I said, 'Now tie up the end of the sack with the lace. Make sure it's good and tight... no. Don't squeeze the air out of the bag. Make sure there's plenty in. It should be inflated when you tie it... good, that's it. Ready?'

She nodded. There was a determined set to her jaw.

I stepped into the water. It was flipping cold. I gritted my teeth. Moving deeper, I tried to ignore the sharp gravel beneath my feet. All the time I scanned the river. It looked particularly dark and somehow evil at this time of night - a deeply sinister abyss oozing with dreadful, nameless horrors.

I realized that more of those water-dwelling triffids might be lurking under the surface. Yet, somewhat rashly, I gambled that the plants either hadn't spread this far or that they favoured the still waters of a lake. From the pull that I could feel round my bare legs the current of the Harlem River was decidedly fierce.

I glanced at Marni. Her skin showed a near-luminous white in the gloom. She gasped and sucked in her stomach at the shock of the cold.

'Don't worry,' I told her. 'We shouldn't be in here long.'

She nodded.

I glanced into her face. In the dark the scar had vanished. What I did notice were her beautiful eyes. They were absolutely trusting. I gritted my teeth and asked myself what fresh dangers I was getting her into.

Something slithered round my knee. I froze instantly. The water was too dark and too muddy to see anything. But I knew I'd felt it. Something smooth and slippery had just brushed against my bare skin.

At any moment I expected to see a sting lash up from the water.

I stood there, stock-still, not breathing, my heart thudding in my chest. Whatever had brushed against me didn't return. It might have been river weed or even an eel. Then again, I didn't want to dwell too closely on what might lurk in that filthy-looking goo.

'Here goes, Marni.' I mustered what remained of my confidence. 'Don't swim yet. Just let the current carry you downriver past the wall. Now, put your arm round the sack and allow it to keep you afloat. OK?'

She nodded, smiling tightly.

'Right. Easy does it. And stay close to me. We've got to keep each other in sight.'

The cold water rising over my body made me clench my jaw. I heard Marni give a stuttering gasp as she lowered herself deeper into the river.

The plastic sack grew taut beneath my arm as it took my weight. Beside me the plastic sack that Marni held gleamed silver. I only hoped the guards on the wall wouldn't notice. A few well-aimed rifle shots would soon put paid to us.

I found I had to paddle slowly with my free arm to keep alongside Marni. And I was right about that current; in moments it had carried us out towards the middle of the channel. Some twenty feet below us would be the slick bed of the river, seething with whatever noxious things had made their home there. In no time at all we were borne downstream, past the boom extension of the wall. Now I could see the bright lights of the city itself. Cars streamed along its roads. I could even see people strolling along a riverside promenade. Night owls were having fun.

Meanwhile, for Marni and I, just fifty yards from the bustling waterfront, the river sucked at our bodies, turning us round, threatening to roll us over and pull us down.

'Grab my hand,' I panted. 'I can't keep close to you.'

Marni raised her hand above the surface of the water. I grabbed it. Held it tight. Now she nodded at the sack I clutched.

It had deflated a little and I looked down to see a stream of bubbles pouring from a nick in the plastic. Nodding, I turned the sack over and gathered the slack plastic into my fist where the gash bled air.

'We'll have to get to the shore,' I whispered. 'I don't want the current to push us across to the other side.' I didn't add that the banks across the water from Manhattan were a congested mass of triffids.

We began to swim, pushing the sacks full of clothes in front of us. Once again something smooth slid across the bare flesh of my belly, nearly fetching a yell from my lips. With a Herculean effort I kept my mouth shut. But shivers like pointed insect feet prickled up my spine and through my hair.

As I swam I expected teeth to sink suddenly into my leg or even, irrationally, a slimy hand to break the surface in front of me and clutch my throat.

But the night swimmer didn't return. We pushed on. I pointed to some bushes over-hanging the water. 'Make for those,' I whispered. 'We should be out of sight of the road.'

The last few yards took a long, long while to cover. A strong current tugged us back, and all the time I expected that invisible denizen of the river to lunge out of the water at my face.

Marni swam hard, the white gleam of the soles of her feet just ahead of me. Moments later I felt something sharp buffet my knees. It came again. I shoved my hand under the water to fend it off - and struck solid stone.

Grateful to have the ground beneath my feet again, I climbed out of the river to join Marni. Exhausted, I sat beside her as she squeezed water from her hair. I'd begun to fumble with the wet bootlace that tied the sack when Marni nudged me, then nodded out at the water.

In the gloom I saw a smooth rounded shape break the surface of the river. It was a glossy liquorice-black. I glimpsed a dorsal fin. Then there came the sound of pent-up breath being released; white vapour flickered briefly above the water.

So there was my monster, my denizen of the deep.

With a smile (and a massive sense of relief) I said, as much to myself as to Marni, 'It's only a harbour porpoise.'

Although I barely had time to enjoy any feeling of deliverance because at that moment an arm abruptly emerged from the bushes to hold the blade of a lethal-looking bowie knife at my throat. More arms appeared to seize Marni and drag her into the shadows.

CHAPTER FORTY.

SOMETHING WICKED THIS WAY COMES...

BUNDLED from the water's edge we were dragged deeper into the bushes. I felt the knife blade pricking my skin. I sensed that any stupid movement I might make would be my last.

A hand grabbed my jaw, pulling my face up towards the light from the street filtering through the branches.

'What should we do with these two lovebirds?' whispered a voice.

'Kill them.'

'But-'

'And be quick about it. Use the knife.'

From another direction came a third whispering voice. 'Wait. I've seen that guy's face somewhere before.'

'So?'

'Hey, it's the guy who flew us here... the English guy... ahm... Masen. That's it: Masen.'

'Are you sure?'

'Yeah, positive.'

More muttered conferring took place. One voice whispered, 'Wait here. I'll be right back.'

'Right back' seemed to take a good half-hour. Meanwhile, our captors kept a grip on us. I saw a glittering knife held to Marni's throat, too. Still soaking wet, I felt myself growing numb with cold.

At last there came a rustling in the bushes.

A voice whispered, 'Sacramento.'

My captor replied with a hissed, 'Berlin.'

More people pushed forward into the bushes. Then a familiar if surprised voice asked, 'David? What on Earth are you doing here?' The hand gripping my jaw released me. I turned to see Gabriel Deeds looking at both Marni and myself in astonishment. A slow grin spreading across his face, he added, 'And why are you naked?'

Quickly, I told Gabriel what happened, including the grim news that the authorities had found our flying boats. As I talked I gratefully pulled my clothes from the sack and put them on. Marni did the same.

Gabriel clicked his tongue when he heard about the planes. 'We'll have to find some other route home. But first things first. We'll get you to another safe house until all this is over.'

'You'll do no such thing. I'm a participant in this venture now. A full and active participant. I'm going to find Kerris and get her out of this place.'

'If she wants to leave.'

'Well, I'm going to hear that decision from her own lips.'

Gabriel nodded. 'OK. But we can't do anything until tomorrow afternoon. All our units are lying doggo until zero hour.'

'Zero hour?'

'That's when the fireworks start. I'll explain later.'

I pulled my flying boots on over my still-damp feet. 'But how did you get down here past the wall?'

'We went underground again.' He glanced at Marni. 'But I guess your guide didn't know about that particular route.' A small smile touched his lips. 'It would have saved you getting your feet wet... as well as sparing your modesty.'

With that, he motioned us to follow him. 'Watch where you're walking. The sappers were setting charges down here when they saw you two frolicking in the river.' He nodded to a concrete block of a building not thirty paces away. 'Anti-aircraft installation, so shhh.' He put his fingers to his lips.

Once we were clear of the bushes I saw that the sappers and Gabriel were wearing casual civilian clothes, enabling them to blend in with the ordinary New Yorkers. Gabriel glanced at Marni's ragged clothes and muttered something to one of the sappers who removed his sweater and handed it to Marni. She pulled it on over her own, concealing its rips and darned holes. The borrowed sweater was absurdly long but at least she looked less like an escapee from the slave camp.

As it was, we didn't have much of a walk. We'd barely gone a block before Gabriel indicated a door beside a still brightly lit cafe. He tapped on the door. It opened an inch or so. Then, when the man on the other side had satisfied himself about Gabriel's identity, he opened the door fully.

Beyond lay a flight of steps. Gabriel led the way downward to a large basement room. Bales of paper filled half of it. Elsewhere there were makeshift beds on a platform of bales. In one corner someone had stacked cases of canned food and bottled water.

'Help yourself to supper,' Gabriel invited us with a wave of his hand. 'It's baked beans cold from a can, I'm afraid. But there's plenty of apple pie and cream.' He smiled. 'I thought we should buy in a good stock just in case Sam Dymes drops by.'

'Where is he?'

Gabriel gave a shrug. 'Away on business.'

I looked at Marni. She'd recovered enough from the night swim to eat a hearty supper of cold beans.

By this time it was three a.m. Over the next three-quarters of an hour more sappers returned from their missions. Straightaway they'd pull off their shoes, then retire to the makeshift beds.

Gabriel handed blankets out to Marni and myself. Then he said simply, 'Big day tomorrow, David. You best get some rest.'

I remember thinking quite clearly as I lay down on the lumpy mattress of paper bales that the one thing I wouldn't be able to do was sleep.

But barely had I closed my eyes, or so it seemed, then I opened them to see Gabriel crouching beside me. Sunlight streamed in from a glazed grating set above my head.

'There's some coffee,' Gabriel said, his face serious. 'Grab a cup, then come over to the table. There're a few details I need to share with you.'

I joined him at the table. Above my head tramping feet on the glazed grille told me that the people of Manhattan were going about their business as on any other day. I glanced to a wall where a clock hung from a nail. Chalked beside it was a message to the unit bivouacked here: Synch Your Watches To This Time. The clock showed that the time was just a little before ten. I'd slept late. Marni smiled and waved to me from where she sat eating from a can. Pleasingly, she'd been given new clothes, while her long red hair shone from what must have been a damn good brushing. Apart from the scar running across her face she would easily have melted into the city's smart set.

Gabriel unfolded a map. 'OK,' he said. 'It all happens this afternoon at five... that's the start of the rush hour. Cars will jam the streets. Workers will be crowding the sidewalks and subways as they head home.' He pointed at the map. It showed the characteristic carrot shape of the island of Manhattan. 'We're here, on the Upper East Side. We know that Christina Schofield and Kerris Baedekker are in the Empire State Building.'

'Does Kerris knows what's happening?'

'She knows that something will happen. But she has no details yet. Torrence has instructed her to be Christina's room-mate to make sure she's happy and entertained before her...' He grimaced. 'Operation.'

'I saw girls being taken off the streets north of the Parallel yesterday. I guessed that was the start of it.'

'You guessed right, David. Any woman capable of bearing a child will be impregnated. North of the Parallel it's mandatory. Down here in the city it will just be considered patriotic... but I figure any woman not volunteering to play host to one of Christina's embryos will be coming under lots of pressure to do so. Now... after the debacle of the last attempt to bring Christina out by submarine Torrence has gone all cagey on us.'

'So Christina won't be moved out to a hospital?'

'No. Torrence has ordered that a suite of offices near the top of the Empire State be converted into a clinic, complete with its own operating theatre. Once Christian's ovaries have been surgically removed they will be shipped to hospitals and maternity clinics ready for the implantation programme.'

'So how do we get into the building to bring Christina out?'

'Good question.' Gabriel assumed a thoughtful pose, his eyes troubled. 'A very good question. We know that it isn't going to be easy. Torrence is very sensitive about his own safety. In buildings immediately surrounding the Empire State he has the bulk of Manhattan's armed forces on permanent standby. They're backed up by tanks and armoured cars. Meanwhile he has his own bodyguard - the Guardsmen - based inside his building. They're a ruthless bunch of thugs who do his dirty work for him.'

'We've got around sixty Marines. You think we're really going to be able to fight our way into what amounts to a fortress?'

'No, we can't simply hammer our way in by brute force.' Gabriel tapped a hefty finger on the map. 'Sam Dymes believes our only chance of success is to draw the bulk of Torrence's army to the far south of the island, down here in TriBeCa and Lower Manhattan. He's going to use a strong detachment of Marines, sappers and undercover operatives to strike at the shoreline gun batteries to make Torrence believe this is the prelude to a big seaborne invasion.' Gabriel gave a grim smile. 'Believe it or not, one of our secret weapons is Manhattan's rush hour. The streets will be choked with cars when we launch the attack on the big guns down there on the river banks. Torrence's tanks and armoured cars will have to travel all the way down from Midtown to Lower Manhattan. The distance is no more than a couple of miles but with luck - and a little more mischief on our part - it will take them an hour to get through the traffic'

'But even so, our Marines are only armed with machine guns at best. They won't stand a chance against tanks.'