As the light fades, an icy wind rises. A southeasterly, racing out of the Gulf of Riga across the Baltic Sea and meeting the ship broadside, so that the containers groan and strain against their lashing rods. Every day, as we voyage eastward toward Russia, the temperature falls.

The container that Villanelle and I have shared for the last five days is a corrugated steel box the size of a prison cell. It's a little over two and a half meters tall, contains a part-load of clothing bales, and sits atop a five-container stack on the starboard side of the ship. Inside, it's as cold as death. The two of us live like rats, huddling together for warmth, nibbling at our diminishing stock of stale bread, cheese and chocolate, sipping our rationed water, and urinating into a plastic bucket. I've been constipated since the ship left port on the northeast coast of England, and Villanelle shits into a series of plastic bags bought from a pet shop, which she then neatly knots and stores.

At the forward end of the container there's an emergency hatch, perhaps thirty centimeters by thirty, which can be unbolted from the inside. This admits a thin shaft of light and a freezing blast of salt air. Standing on the clothing bales, my eyes streaming, I watch the steady rise and fall of the horizon and the slow-motion leap of the bow wave, white against gray, until my face loses all feeling. When the wind drops, I'll pour the piss-bucket out of the hatch. It'll freeze as it runs down the container. I've asked Villanelle to throw her shit bags out too, but she's worried that one might land on deck.

She's thought of everything. Thermal vests and leggings, underwear, toilet paper, washing stuff, tampons, neoprene gloves, red-light torches, a commando knife, plasticuffs, 9mm ammunition for her Sig Sauer and my Glock, and a hefty roll of used U. S. dollars. We have no phones, laptops or credit cards. No identifying documents. Nothing to leave a trail. No one except Villanelle knows for certain that I'm alive, and Villanelle is officially dead herself. Her grave, marked with a small metal plaque provided by the Russian state and inscribed Оксана Воронцова, is in the Industrialny cemetery in Perm.

Two years ago I didn't know that Villanelle, or Oxana Vorontsova, existed.

I was in charge of a small inter-Service liaison department at Thames House, MI5's London headquarters, and life was, on balance, fine. Work was on the dull side: I had an MA in criminology and forensic psychology, and had hoped for a more challenging deployment with the Security Service. On the positive side I had a steady if unspectacular income, and my husband Niko was a kind and decent man whom I loved, and with whom I was hoping to start a family. There were worse things, I told myself, than routine, and if I spent every spare moment at the office building up a file of unattributed political assassinations, it was just a private thing. Just me keeping my hand in. A hobby, really.

In the course of this unofficial research I became convinced that several of these killings had been carried out by a woman, and almost certainly by the same woman. Normally, I would have kept this theory to myself. My role at MI5 was administrative, not investigative, and there would have been raised eyebrows and condescending smiles if I'd brought the subject up with my superiors. I'd have been regarded as a slow-lane liaison officer getting above herself. Then a Russian far-right political activist named Viktor Kedrin was shot dead at a London hotel, along with his three bodyguards. I was accused of failing to organize adequate protection for Kedrin, and fired.

This was bitterly unjust and everyone involved knew it. But we also knew that when the department fouled up as royally as this, and it didn't get much worse than the assassination of a high-profile principal like Kedrin, someone had to take the fall. Ideally, someone senior enough to count, but not so senior that they couldn't easily be replaced. Someone expendable. Someone like me.

Shortly after I'd cleared my desk and handed in my pass at Thames House, I was discreetly contacted by a long-serving MI6 officer named Richard Edwards who, unlike his counterparts north of the river, was prepared to listen to my ideas. Seconded to his off-the-books team, and tasked with finding Kedrin's killer, I pursued Villanelle around the world. She proved a spectral and elusive quarry, always one flawless step ahead. All I could do was follow the blood trail. And, unwillingly, admire her grim artistry. She was bold, free from guilt or fear, and probably a little bored by the ease with which she evaded detection. Flattered to discover that I was pursuing her, Villanelle began to do the same to me. One night in Shanghai, she climbed up the outside of my hotel into my room and stole my bracelet as a trophy. To make amends, and for the sheer effrontery of it, she broke into my house in London in broad daylight, to leave me a different (and much more expensive) bracelet that she'd bought for me in Venice. These intrusions were as flirtatious as they were terrifying. Whispered reminders that she liked me, but could kill me at any time she chose.

Although I refused to admit it at the time, even to myself, this twisted courtship had its effect. Obsession is not immediate. It stalks you. It creeps up on you until it's too late to escape it. When I first saw Villanelle in person it was by chance, and again it was in Shanghai. I was on a scooter, caught in traffic, and she was walking down the pavement toward me, dressed entirely in black, with her blond hair slicked back from her face. Our eyes met, and I knew it was her. Villanelle can be sweetness itself when she chooses, but that evening her gaze was as flat as a snake's. She claims that she recognized me on that occasion, just as I recognized her, but I don't believe her. She lies. She lies compulsively, all the time. Later that night she lured my colleague Simon Mortimer into an alleyway and hacked him to death with a meat cleaver. The savagery of the attack shocked seasoned investigators of the Shanghai homicide squad, who had seen their share of Triad killings and other horrors.

Our second meeting, on the hard shoulder of a motorway in England, was orchestrated with chilling brilliance. I was driving back to London from a Security Services interrogation center in Hampshire. My passenger was Dennis Cradle, a senior MI5 officer who, earlier that morning, had admitted to me that he was in the pay of the Twelve, the organization that employed Villanelle to do their killing. I'd tried to turn Cradle, to get him to inform on the Twelve in return for immunity, and he'd responded by trying to recruit me, which was pretty fucking cheeky, all things considered.

Twenty minutes into the journey, we were flagged down by a female police officer on a motorcycle. It was Villanelle, of course, but by the time I'd figured that out, it was too late. Villanelle told me that she'd missed me. Touched my hair, and talked about my "pretty eyes." It was all rather romantic, in its way. Then she disabled my car and abducted Cradle, leaving me stranded beside the motorway. Cradle probably thought he was being rescued. In fact, Villanelle drove him to a secluded spot outside Weybridge, smashed the back of his skull with a blunt instrument -- I'm guessing a police-issue baton -- and dumped him in the River Wey.

Villanelle wasn't ideal girlfriend material, but then I wasn't looking for a girlfriend. I was married, for heaven's sake. Happily married, to a man. And if sex with Niko had never been transcendent -- no flaring comet-trails or exploding supernovae, no werewolf howls -- I had no complaints. He was that rarest of beings, a genuinely good guy. He loved me when no one else gave me a second glance. He praised my hopeless cooking, was enchanted by my fashion-blindness, and regularly assured me, in the teeth of evidence to the contrary, that I was beautiful. In return, I treated him appallingly. I knew exactly how much I was going to hurt him, and I did it anyway.

It was the way Villanelle made me feel. For all my frozen horror at what she had done, I was awestruck. Her focus, her meticulousness, her ruthless purity of purpose. I'd been sleepwalking through life and suddenly there she was, my perfect adversary.

I would learn later that Villanelle had felt the same way. That while working as the Twelve's star assassin had its professional and material rewards, she had begun to crave an excitement that routine political murders didn't deliver. She had developed an appetite for danger. She wanted to lure a pursuer onto her trail, someone worthy of her mettle. She wanted to dance on the razor's edge. She wanted me.

Niko loved me, and I'd always felt safe in his arms, but the games that Villanelle played were satanically addictive. It took Simon's murder to awaken me to the boundless range of her psychopathy. I hated her after that, which was what she intended. She wanted to show me the worst of herself, to see if I'd back off. Of course I only came after her all the harder, which delighted her, but then Villanelle never drew any distinction between hate and desire, between pursuit and courtship, and in the end, neither did I.

When did I lose perspective? Was it in Venice, when I discovered that she'd been there a month earlier with another woman, a lover, and I found myself transfixed with jealousy? Or was it earlier, by the side of the motorway, when she told me that after climbing into my hotel room on that monsoon night in Shanghai, she'd sat and gazed at me as I slept? It doesn't matter anymore. What matters is that when Villanelle asked me to come with her, to walk out of my life and leave behind everything and everyone I'd ever known, I did so without hesitation.

I knew, by then, that I'd been living a lie. That from the time I'd first been approached by Richard Edwards, I'd been brilliantly, artfully deceived. When Richard asked me to investigate Villanelle and the Twelve I flattered myself that he was impressed by my intuitive and deductive skills. In fact he'd been a fully paid-up asset of the Twelve all along, and wanted to use me to test the organization's security. It was a classic false flag operation, and by conducting it off the books, for reasons that made perfect sense to me at the time, he ensured that no one at MI6 got wind of it.

I had begun to suspect that I'd been used in this way, but it was Villanelle who finally confirmed it. She's a psychopath and a habitual liar, but she was the only one who told me the truth. She showed me, dispassionately, just how easily I'd been manipulated. Listening to her was like watching an elaborate stage set being dismantled, and suddenly seeing ropes and pulleys and raw brickwork. She told me that she'd been given her next target, and that it was me. I'd discovered more than I was meant to. I wasn't the Twelve's dupe any longer, I was a liability.

The encounter, and its aftermath, was classic Villanelle. I'd just returned from a horrendous few days in Moscow, and when I got back to my flat I found her in the bath, washing her hair. A 9mm Sig Sauer was lying between the taps, and she was wearing latex gloves. I was pretty sure she meant to shoot me. Villanelle is coy about how many people she's killed. She just says "normal amount," but I'd guess that the figure is nineteen, maybe twenty victims.

We had to stage my death. Then we had to disappear.

So that's what we did, and soon we were racing through the night on her Ducati motorcycle, my arms wrapped tightly around her, heading north. Villanelle didn't really give me a choice, but then I didn't want her to. I was ready to cut the ground from beneath me. I was ready to fly.

I've often wondered, since that day, what would have happened if I'd stayed. If I'd begged Niko's forgiveness, and gone to the police, or perhaps even the newspapers, with my story. Would I have survived? Or would it have been the car that didn't stop, the heart attack on the way to the supermarket, the apparent suicide? And if the Twelve had finally decided that I wasn't worth killing, and had engineered things so that I looked and sounded like a conspiracy theorist, just one more recruit to the sad, twilight army of the deluded, would Niko ever have trusted me? Or would I have forever felt his eyes on me, watching and wondering, as we made small talk over dinner, or endured endless evenings at the bridge club?

We stowed away at Immingham, a port in Lincolnshire. It cost us the motorcycle and the remains of my dignity. The guy was a deckhand, on shore with a crew visa. We hooked up with him in a pub outside the terminal, a fake Irish establishment so depressing it was almost funny. We'd been nursing a couple of beers for the best part of an hour when the guy came in. Villanelle clocked him as Russian straight away, swung over to his table, and went to work. His name was Igor and his ship, as we'd hoped, was the Kirovo-Chepetsk, a Panamax-class container vessel bound for St. Petersburg. Villanelle didn't waste any time. Poured a triple vodka into him and made her pitch. Igor didn't look too surprised.

When we took him outside to see the bike, it had started snowing. Villanelle unzipped the waterproof cover, and Igor gave a low whistle. I don't know one end of a motorcycle from the other, but the Ducati was a thing of beauty and riding on it behind Villanelle had been a dream.

"Want to try her out?" Villanelle asked, her breath vaporous. Igor nodded, slowly running his hands over the handlebar controls and the volcano-gray tank. Then he swung a leg over the saddle, thumbed the ignition switch, and took off on a whisper-quiet circuit of the car park, snowflakes whirling in the headlight beam. When he dismounted, clearly smitten, Villanelle pressed home her advantage in fast, idiomatic Russian. He answered in a murmur, shifting his weight uneasily.

"He'll get us on board tomorrow night," she said. "But the bike's not going to be enough. He'll do prison time if he's caught."

"What else does he want?"

"He wants to see your…" She nodded at my chest.

"My… No. No way!"

"Just one photo, for his private use. He says you remind him of his Aunty Galya."

"Are you fucking kidding me?"

"No. She drives a tram in Smolensk. Get them out."

I looked around the car park. There was no one, except for the three of us. Unzipping my leather bike jacket, I pulled up my sweater, thermal undershirt and bra. Fuck, it was cold.

Staring, Igor fumbled in his track bottoms for his phone. It took him the best part of a minute of crouching and weaving to get the shot he wanted.

"Just make sure my face isn't in the picture," I said, shivering. Snow was blurring the lenses of my glasses.

"He's not interested in your face. He says you have nice breasts, though. And I agree."

"Well it's nice that you're both having such a lovely time, but I'm literally freezing my tits off here. Can I please get dressed?"

"Yeah, we're good. He'll help us."

"When do they load this container onto the ship?" I whispered, as we hollowed ourselves out a nest in the clothing bales.

"Tomorrow, the driver said. Probably around midday."

"Do you think anyone will check inside first?"

"They might. Are you afraid?"

"Right now, I just don't want us to be caught."

She said nothing.

"How long have you been planning this?" I said.

"I've always known that one day things might change and I might have to run. So I worked out escape routes. What I didn't plan for was you coming too."

"Sorry about that."

"It's OK. Your spoken Russian is shit, so when we get to St. Petersburg you can be mute. Maybe weak in the head. Maybe both. Take your leathers and boots off."

"Why?"

"So you have something to put on tomorrow when you wake up. Also we have to keep each other warm, share body heat. Do what I say."

"Please," I said.

"Please what?"

"Please do what I say."

She jerked herself away from my side. "Fuck 'please,' suchka. You want to stay alive, you obey me."

"I see."

"Obviously you don't see. This is my world, OK?"

"It's mine too, now. Whether I want it or not."

"You want to leave? Fine. See how long you last, yebanutaya."

I couldn't see her. But I sensed her fury, radiating through the darkness.

"Villanelle," I began. "Oxana --"

"Don't ever call me that."

"OK, I'm sorry, but --"

"But nothing, Polastri. I hope you freeze. I mean it, I hope you fucking die."

I undid my jacket, trousers and boots and placed them where I could find them in the dark. Beside me, I could hear Villanelle doing the same. Shivering, I settled myself into the bales, about a meter away from her. As the minutes crept by, and the cold wrapped more and more tightly around me, I listened to the calm rise and fall of her breathing. Hateful bitch.

What was I doing? Why, knowing everything that I knew, had I trusted her? I clamped my teeth together, but was unable to prevent them chattering. I pressed my hand over my mouth, blinking away tears of hopeless, abject fury, and knew that I'd destroyed everything in my life that had value. That I'd ignored the inner voice that might have saved me, and thrown in my lot with an unfeeling monster who killed people without a second thought, and who would probably, sooner or later, kill me.

I wiped my nose with my sleeve, and sniffed. A heartbeat later I felt Villanelle shift. She molded herself against me, her knees behind mine, her breasts against my back. Nudging my hair out of the way with her nose, she pressed her face against my neck. Then she folded her arm over mine and arranged her fingers around my wrist. I was still shivering, and she moved more closely against me.

Finally, as the warmth of her body possessed me, I was still. Silence enclosed us, and I imagined the snow beating at the container's walls and roof. My arm twitched, as it sometimes does at night, and Villanelle's hand closed around mine, her thumb firm in my palm. Taking a tress of my hair between her teeth she gently tweaked it, then licked the nape of my neck as if she were a lioness. And bit me, hard.

I arched away from her, gasping, but she grabbed my shoulders, swung me onto my back, and pulled herself on top of me so that we were face to face in the darkness, her breath beer-sour, her nose cold against my cheek. Then her tongue was in my mouth, snaking and probing. I twisted my head away. "Stop."

"Why?"

"Just… talk to me."

She rolled onto her side. "What about?"

"Have you ever really cared, really felt anything, for another person?"

"You think I can't feel?"

"I don't know. Can you?"

"I feel like you feel, Eve. I'm not some freak." She took my hand and pulled it into her panties. "Feel my pussy. Wet."

It was. I left my hand there for a single, dizzying heartbeat. "That's not the same as caring about someone," I heard myself say.

"It's a good start."

I steadied my breath. "So have you ever been in love?"

"Mmm… Sort of. Once."

"And?"

"She didn't want me."

"How did you feel?"

"I wanted to kill myself. To show her."

"So where am I, in all of this?"

"You're here, dumbass. With me." Her fingers found my hair. "And if you don't kiss me right now, I really am going to kill you." She started to pull me toward her, but I was already there, searching for her mouth with mine.

Then we were all over each other, bumping noses, smearing lips, and blindly, desperately kissing. I felt her fingers hook into the waistbands of my thermal leggings and panties and drag them over my ankles, and as she moved back up my body I tried to pull her sweater off, but the neck was so tight that she fell on top of me, laughing and whispering that I was choking her. Sitting astride me, she inched the sweater forwards over her head. It brushed my face -- warm wool, stale sweat -- and then it was gone, and her undershirt and bra after it. She pulled mine off and I shuddered as the cold seized me. "We need to toughen you up, pupsik," she whispered, wriggling out of her own leggings and panties.

All was rapt discovery. Her skin and my skin, her smell and my smell, her mouth and my mouth. Villanelle took charge, as I needed her to, and I felt her hand reach confidently between my thighs. She'd killed a man with a knife-thrust through the femoral artery. A strike so delicate, so surgically precise, that her victim was probably not immediately aware that he'd been stabbed. Could she feel the throbbing of my femoral artery? When she slid those fingers inside me, was she remembering other, bloodier penetrations? Did the warm explorations of her tongue recall more lethal partings of flesh?

Afterward we pulled our sweaters and jackets on top of us, and I folded into her back, spoonwise. For several minutes I lay there in the dark, overwhelmed, my lips touching the soft hair on her neck, which stirred as I breathed.

"It's weird," she said. "I can't remember what you look like."

"Not at all?"

"No. You could be anyone."

I raised myself on one elbow. "Why do you like me? Truthfully?"

"Who says I like you?"

"Don't you?"

"Maybe. Maybe I just wanted to get into your pants. Which, by the way, are not pretty."

"Ah."

She wriggled her bottom against me. "Truthfully, I have a thing for dorky women. Especially in glasses."

"Thank you so much."

"Pozhaluysta. I need to pee."

She did so, noisily, into the bucket, which she'd lodged in the clothing bales in one corner. I followed her there and did the same, not easy in the dark, then we dressed ourselves -- it was just too cold not to -- and I curled up behind her again, with the sharp smell of her hair in my face. "Admit it, pupsik," she murmured, barely audible, "this is a much more romantic honeymoon than your first one."

We woke the next morning as the truck shuddered into life and began its journey to the docks. We lay motionless, the only sound the slopping of the urine in the bucket. Twenty minutes later we came to a halt, and I felt Villanelle's body relax and her breathing become slow and calm. This was the moment of maximum danger. If there was to be an inspection of the container and its cargo, it would be now. I tried to imitate Villanelle's zen state, but started to tremble uncontrollably. My heart was pounding so wildly I thought I was going to pass out.

A dull clang reverberated throughout the container. I burrowed desperately into the bales, ignoring a brief explosion of pain as my nose struck Villanelle's forehead or shoulder. The truck began to move again, but I stayed submerged, inhaling the thick smell of unaired cotton. This time the journey was shorter, our stop-start progress indicating that we were in a line of vehicles approaching the loading bay. With the final halt, the truck's engine fell silent. There was a harsh scraping of metal on metal, a heavy thump, and we started to ascend. I'd dreaded the moment the container was hoisted from shore to ship, picturing it swinging sickeningly beneath the cranes. Nothing of the sort happened, of course. The process was smooth and deft, with only a brief kiss of steel to indicate the moment we were locked in place, and a faint knocking as our temporary home was fixed to those beneath it.

Hours passed, during which the smell of urine grew stronger, and Villanelle maintained an unapproachable, trance-like silence. Was she telling herself that she'd made a fatal miscalculation in bringing me with her? Had the previous night meant nothing to her at all? I lay there, staring into the cold darkness. Finally I slept.

I woke to the steady thrum of the Kirovo-Chepetsk's engines and the faint creak of the containers around us. As I regained my bearings, Villanelle's hand reached through the darkness and found mine.

"Are you OK?" she whispered.

I nodded, still not quite there.

"Hey. We're alive. We got away."

"For now."

"Now's all there is, pupsik." She pressed my palm to her icy cheek. "Now's all there ever is."