A quick glance round let him see the tower, a black phallic monolith probing a cloud-smeared night sky. The first floor's broken window was a glaring yellow rectangle, while others glowed with biolum's softer pink-white radiance; sketchy shadows were moving about inside. Several people were dashing about on the grass ring around the tower's base; three were splashing through the shallows, but not venturing far. If they wanted to get across to the reeds they'd have to get down on their bellies and squirm; it was the only way. They didn't have the motivation. A couple of intense torch beams stabbed out, scouring the reeds.

Greg rolled back on to his stomach and began his serpent wriggle again. Thirty seconds later there was hard ground under his elbows. Reeds competing with stiff blades of grass. He was using his knees as well as his elbows now, scuttling towards the gable end, and cover. He knew exactly what Kendric and Armstrong would do next. Flinty pebbles and rapier grass lacerated his skin. Somewhere over to his left another heavy body was burrowing through the vegetation.

An electromagnetic rifle opened up, warbling loudly. Bullets thudded into the mound, pinged against the brickwork, ricocheted off, whining. Greg kept going.

"Get over there." That was Kendric's unmistakably enraged voice. Murmurs of argument followed.

The white torchlight trimmed the tips of the reeds around Greg. Tiny reddish-brown ovate flowers glowed lambently. Midges formed a silver galaxy overhead. The light passed on. The electromagnetic rifle had fallen silent.

Greg reached the sloping brickwork. Gabriel was ahead of him, panting heavily at the end of a streaky mud trail.

"God, the smell," she exclaimed.

"What smell?"

"Some people."

He climbed gingerly to his feet. The island they were on was about twenty metres at its widest. Greg had cherished a half-notion that the mounds would all be connected. But the next one was a good forty metres away. Algae-curdled water sloshed like crude oil between the two. It didn't look as though there was much of it on top of the mud.

"Clothes off," Greg said, then flinched as the electromagnetic rifle poured another fusillade of bullets into the gable end.

"Do what?" Gabriel asked. She was cradling her left hand again. Her face was haggard, totally lethargic.

"We've got a lot of swimming to do. Clothes are going to drag us under."

"Swim where?"

"Clear of the tower, remember? Kilometre at least. How long have we got?"

Gabriel closed her eyes. "About twenty minutes, maybe less."

"Do we survive?"

"Some of us do, some of us don't." She sounded completely disinterested.

Greg ducked his head round the side of the bricks, bringing it back fast. "Bugger!"

"Now what?"

"They've put the fire out. I was hoping it would be a beacon to the ships on the Nene. Somebody might report it."

That brought a half-hysterical giggle from Gabriel, ending in a gurgling cough. "Don't you worry, Greg. Lots of people are going to see your tower before tonight's out. You betcha."

"Oh, yeah." He felt stupid. "Let's go." He started shrugging out of the dinner jacket, clenching his teeth as his left hand dragged through the arm, it'd swollen badly, skin stretched taut, pulling open the grazes. Trousers followed, and the discovery that buckles are tricky one-handed.

More shouting had broken out from the tower. Lots of conflicting orders interwound with Kendric's repeated urgings and Armstrong's controlled barks.

Gabriel gave him a remorseful stare before starting half-heartedly on the buttons of her blouse. Greg peeled his trousers off and helped her pull her blouse gingerly over her inflated left hand.

"Put your shoes back on," he said.

A third burst of rifle fire lashed the bricks.

They bent double, keeping the bulk of the small pyramid between themselves and the tower as they crept down to the grey slime. The stuff was semi-liquid, a thick gelatine that squelched and undulated alarmingly as Greg immersed himself. It closed around him, finding its way into every orifice. But he didn't sink. In fact the worst of it was on the surface. A sixty-centimetre stratum of water had been sandwiched between the spongy mud and lathery algae.

Gabriel groaned as she lowered herself behind him and the cold mire enveloped her.

Greg began to move, a tortuously slow sidestroke, kicking hard with his feet. Big faecal gobs of the pulpy algae clotted his right arm, splattering over his face. He had to stop every four or five strokes and wipe it off. His eyes were stung raw. Gabriel had it easier. He was path-breaking for her, clearing a ragged channel.

When they reached the second island, Greg began to worry about what kind of chase was being organised back at the tower. He looked over his shoulder and saw that someone had opened the tower's top-floor window, they were raking the torch beam over the first island and the surrounding water. The light wasn't powerful enough to reach him, but he made Gabriel keep below the wavering tops of the thin reeds as the pair of them crossed over to the island's opposite side.

Away to the right, Greg could see the bloated humps of decomposing tree trunks protruding from the algae like surfaced whales. The number, about thirty, implied some sort of park, which ruled out that direction. They needed to move fast now. Build distance before the tower blew. The park would be genuine swamp, impossible to traverse.

A hundred and fifty metres ahead were the first ranks of buildings recognisable as such; detached houses, their walls partially collapsed and roofs concave, but remaining upright. Bridging the gap was a pockmarked landscape of ash-green atolls separated by hoary stretches of slough.

"Any preference direction-wise?" Greg asked.

Gabriel shook her head. "No. But you were right about getting clear. That explosion is a brute. I hope I can make it."

She was a state. Loose folds of flab were caked in thick sable mud, her hair was a tangle of ossifying dreadlocks. Every breath was asthmatic, a battle against coagulating catarrh. She twitched like a palsy victim.

"No problem," he said, wishing to God he meant it.

They waded into the first slough channel.

The fifth island they came to was much larger than the previous four. Iron girders were sticking out among the sedges. There was more grass than reeds on the crest. Soil had begun to accumulate in the crevices between the fragments of stone and cement. Greg cut his calf on something jagged. Cursed.

The island's far shore brought them to within thirty metres of the houses. One more immersion and back on to solid ground. This time it was a long straight ridge parallel to the row of houses. It was cluttered with twisted, drooping chimney stacks, and buckled rafter apexes gnarled with scabby lichens; slate tiles formed a loose flaky shingle beneath their feet, making the going hard.

Just as he reached the summit, Greg heard the sound. A low-volume hum in the background. But rising in pitch and intensity, in menace. A note he was irksomely familiar with.

"Move out, double-time," he said. "The bastards have inflated the hovercraft."

"No more," Gabriel said wretchedly.

"One last time. That's all. Then it'll all be over."

"Yes. Yes, you're right. Only a few minutes left. It's clearing, Greg. So much clearer now."

Realisation struck. He could sense her mind. A pale disconsolate mist of disjointed thoughts, fluttering aimlessly, corrupted with coarse threads of harrowing pain. Gabriel was animated by adrenalin alone, and her endocrine glands were virtually exhausted.

They'd escaped the twins' nullifying effect. Greg let his gland run riot, charging his cerebellum to overload, and screw the risk. Synapses vibrated shrilly under the stress, delusional ripping sounds filtered into his ears, coming from inside his skull, neurone membranes splitting open. His espersense swept out. It was a heady boost. Whole once more.