We woke to grey skies and rain on the window. We knew we were going to have to cut our holiday short, so we got dressed and drove down to the sea for a last look. We had our suitcases on the back seat of the car, and it was raining as we pulled into the car park above the beach. Wet pebbles clicked and scattered beneath our wheels.

"Come on," Debs said. She opened the door and ran over to the slippery concrete steps that led down to the beach. Her thin summer dress streamed and flapped around her legs as she ran.

I pulled my coat on and followed her. But by the time I reached the foot of the steps, she was already down by the waterline, shoes in hand. As I watched, she stepped out of her clothes and waded into the waves.

"We don't have time for this," I called.

She ignored me and slid out into deeper water. For a moment, I lost her in the surf, and then saw her bob up between the waves, spluttering and laughing. She pushed her wet hair back, and the water glistened on her skin.

"Come in," she called. Then she turned and struck out parallel to the beach, swimming with strong, graceful strokes. I leaned against a rock and watched her for a few minutes. Then I started walking back toward the car. The rain made little pockmarks in the wet sand. When I reached the wooden steps, I called to her.

She came splashing out of the shallows.

"Where's my dress?" she said, looking around for it.

It lay on the sand, where it had been dropped; the water tugged at it.

"Forget it, it's wet," I said. I slipped my coat around her shoulders and she laughed.

"You're such a gentleman."

We climbed up to the car. I could smell the salt in her hair.

"That was wonderful," she said, shivering.

I unlocked the doors and slid in behind the steering wheel. She stretched out on the passenger seat. The windows started to mist, so I put the heater on.

"We'd better get going," I said.

She wrinkled her nose. "Do we have to? Can't we go somewhere else?"

I shook my head. "The bombing starts in an hour. And besides, you've only got a coat on--where were you thinking of going?"

We followed the A3083 for a few miles, occasionally passing convoys of armoured vehicles heading south. While I drove, Debs leaned back and brought her sandy feet up to rest on the dashboard. The coat fell open, showing off her slender legs.

"Are we out of cigarettes?" she said, checking the coat's pockets.

"I'm afraid so."

Where we were going--into the overcrowded refugee camps of Bristol and Bath--little luxuries like tobacco, alcohol, or toilet tissue were going to be worth their weight in gold.

"Maybe it's time we gave up," I said.

She patted my leg.

"It'll do us good." she said.

The road passed through a deserted village and dropped into a shallow valley. I downshifted for the winding climb back out.

Debs was still stretched on the seat. She turned to look out the side window, and I admired the way the tendons in her neck moved smoothly beneath the skin.

"We just need to learn to relax," she said.

We'd been in Cornwall for six days, spending time away from the city, somewhere her father couldn't find us.

We'd been staying in the spare room of a cottage owned by a friend of mine called Phil. He was a technician on one of the large antenna dishes at the Goonhilly receiving station.

We were there in his kitchen the night he came home raving about the anomalous satellite signal they'd picked up, the one that caused strange effects in the soil around the giant dish. And we were there the next morning--a Sunday--when they called him in to work, when they first started using words like 'quarantine' and 'sensible precautions'.

Two days later, the army started evacuating the surrounding villages.

"Is this something to do with that monkey that ate the Internet?" Debs asked.

Phil shook his head. "No, this is something new."

We were passing between ploughed fields, heading north on the Falmouth road.

"Can we stop somewhere?" Debs asked.

I looked at the clock on the dash. "We don't have time. We're supposed to be out of here already; we're really pushing it."

She reached out and touched my cheek. "Please?"

I pulled the car off the road, into the shelter of an unruly hedgerow.

When I turned off the engine, I could hear the sound of helicopters somewhere off to the west. The road was empty.

Debs refastened the coat and got out. She took my arm and led me over to a five-bar gate that opened into a ploughed field.

"There's a wood over there," she said, pointing across the field, and I sighed, already knowing what would happen.

She squeezed my arm. "You don't need to sound so resigned," she said.

I helped her across the field. The thick, sticky mud made walking difficult.

"You should take your shoes off," she said, "or you'll ruin them."

When we reached the trees, she let go of my arm. She skipped ahead, humming a bright, disjointed tune, hopping and prancing with her bare feet like a ballerina.

I looked at my watch and cursed her. We should have been long gone by now; if an army patrol pulled us up, we could be arrested, or shot.

I glanced back at the car, and Debs danced off, into the trees. I could hear her somewhere nearby, crashing and stumbling around in the undergrowth, but the rain deadened the sound and I couldn't tell for sure where she was.

I hesitated.

"Where are you?" I said.

Above, disturbed crows flapped into flight with hoarse, protesting cries.

I heard a giggle, a snapped twig, and I swore under my breath. I was annoyed and uncomfortable without my coat, and in no mood for one of her games. My shirt was wet and the cold air seemed to cut right through it; my feet were balls of mud.

"Where are you?" I asked again.

She laughed, but didn't reply.

Angry, I waded into the undergrowth, swinging a damp stick to beat down the nettles. Brambles clawed at my trousers. I blundered forward a short way, and then leaned against a gnarled tree. The rain smacked against the higher branches and dripped and trickled down to the mossy floor.

"I'm going to count to ten," I said, "and then I'm leaving."

There was another giggle, and I caught a glimpse of colour through the bushes to my right. I pushed forward and found my coat hanging from a low branch. I took it down and fished my mobile from the pocket. Its solid plastic casing gave me some reassurance. I unlocked the keypad and checked my messages. There were two--one from my editor and the other from my ex-wife. They were both worried. We were still in the quarantine zone; more villages were being evacuated, and they wanted to know if we were all right. I thought of calling them, but couldn't get a decent signal.

Debs's mirrored sunglasses were in the other pocket.

"You'd better come out," I said.

There was a rustle of leaves off to my right. She said, "I don't want to go into one of those dreadful camps, I want to stay here."

She came out from behind a bush. She wore a string of ivy around her neck. Her arms were folded and her hair plastered to her scalp.

"You'll get pneumonia," I said.

"I don't care."

She sat down and put her chin on her fist. Black dirt and wet leaves stuck to her skinny thighs. Her feet were still caked from the field.

"I want to stay here," she said. She wrapped a finger in the ivy hanging around her neck. I walked over and covered her shoulders with the coat.

"We can't. You know there's something happening. We've got to get out."

From the southwest came a series of dull, rolling thuds. She shivered again.

"Listen," I said. "They've started bombing Goonhilly."

She pulled me deeper into the trees.

Eventually, we came to a lake near the far edge of the wood. The water was a dark, vegetable green. The rain had eased into a clinging drizzle. She put her bare arms around my waist. I could feel the heat of her through my shirt.

"Let's swim," she said.

I pulled away. "Aren't you wet enough already?"

She laughed, and reached up to touch my face.

"You should try it."

She handed me the coat and put her hands on her hips.

"You know, you used to find this kind of thing exciting," she said.

I looked into the still, dark water. Overhead, jets roared through the low clouds.

I thought about her father. I thought about work on Monday. And then I thought about the alien plague eating its way into the Cornish soil.

"Things change," I said.

She bit her lip and turned away. I watched her wade into the shallows. I watched the green water wash the clinging dirt and dead leaves from her legs.

When she got up to her waist, she turned and asked me to follow. And there was something in her voice I hadn't heard before, something that shattered my resistance.

Without knowing why, I put one foot in the water, and winced as it oozed into my shoe.

From the direction of the road, I heard the roar and clatter of approaching tanks.

I said, "We're going to be in a lot of trouble if we get caught."

She held out a hand. "It doesn't matter."

I put the other foot in, and thought: What the hell am I doing?

I stumbled out into deeper water and fell forward, swimming as best I could. The cold made me gasp. The water smelled rotten. I splashed toward her.

And then I remembered my mobile, still in my coat pocket, now ruined.

"Good," she said. "You're doing well." She leaned back and kicked out toward the centre of the lake.

I said, "It's getting deep."

There were fresh explosions from the southwest, closer than before. My hands and feet were tingling.

"The water feels strange," I said.

"It's okay," she replied. "Just relax."

I struggled on a bit further. My arms ached and I could feel the tingle spreading over my skin, like a rash.

"What's happening?" I said.

Debs stopped swimming.

"It's the 'plague from the stars'--it's in the water," she said, smiling.

I tried to turn around, to get back to the shore, but she caught my foot.

"It came to me in the sea," she said. "It's spread further and faster than anyone knows. And it spoke to me--it said there's nothing to fear, nothing at all."

I tried to get away, but it took all my strength just to stay afloat. The dead weight of my wet clothes dragged at me, pulling my head under the water. I kicked my legs in panic, felt a shoe fall away.

I said, "Help me!"

But Debs drew back, raised her face to the rain.

"Just let go," she said. "You won't drown. You'll just become a part of it, like I am."

I struggled toward her, got a hand on her shoulder. It felt hot and slippery. Desperate, I said, "I love you, you know."

She laughed, and wrapped her fingers in my hair. We were a long way out from the shore.

"I know," she said.