Nat Marley didn’t bother tipping the taxi driver and he certainly wasn’t going to thank him — it just wasn’t his style. The guy was doing his job, he didn’t need thanking for that, and he only tipped if they did something exceptional for him, or he was trying to impress some pretty little thing he’d picked up. Other people often accused him of being cheap, waiting for his change when he had enough in the bank to support a small country, but it was the principle of the thing for him. Give nothing away for free.

He slammed the door and stood in front of the tall glass building. It was a building he knew well enough, he had walked past it every day for the last five years. Eisenberg, Katz & Frey were the company he had set his heart on getting into ever since graduating, and it looked like he was finally going to get his chance. He’d heard of the top companies poaching the elite from their competitors before, and there was often a good sweetener to help you jump ship. Not that he needed any kind of sweetener, just getting a foot in the door was exciting enough. This was where he would make his real fortune, he was sure of it, and he could put the stress of the last year behind him.

Almost a year ago, he had stupidly involved himself in some extra-curricular activities that had seemed like a good deal at first — he had been approached by a group of likeminded individuals to pool their resources to build a program that would tackle the security vulnerabilities in their part of the financial sector and make them all richer than they could imagine. They had called themselves The Water Boys, and they fancied themselves as the best of the best. He had been paid well for his time, but had gradually begun to realise that they were working on something much bigger than he thought, and he didn’t like the risk of it. He knew that their industry was more complacent about security than it should be, but he wasn’t prepared to become an activist to prove it. When he realised that the people he had joined forces with were actually looking to bring down the stock markets, he tried to pull out. That was when the threats had begun. He had given them one last piece of code, but it had deliberately included a backdoor, in case they ever used it. He had assumed that his involvement was now over, and he had then set about building the antidote. If they did attack the market, it would be Nat Marley who stopped them. He would become a legend. Tonight’s meeting would be the beginning of that journey.

Nat Marley might be young, but he was widely recognised as one of the most gifted employees in his firm right now, and he knew it. He had graduated top of his class, which was already an elite group of mathematical geniuses, and after a brief stint on Wall Street, he had been snapped up and shipped back to London by Flintlock and Staines, one of a handful of high-frequency trading firms which effectively ruled the London Stock Exchange.

People have an image of the stock market which usually involves testosterone-fuelled men in expensive suits and colour-coordinated shirts, barking orders into multiple telephones, while watching fluctuating market prices appear and disappear on a scrolling ticker-tape beneath large banks of screens. That image is as outdated as the movies that created it, but the alternative is too complex for most people to comprehend, so we cling to the old image because it makes sense. It puts people behind the success and failure of our stock market, and somehow that makes it okay. The truth is that those traders are no longer there, at least not in the same way, and the majority of trades are now made inside black boxes, located in heavily-guarded buildings, with little or no human understanding of what happens.

Following the market collapse of October 19, 1987, which became known as Black Monday, the global financial industry began to change irrevocably. The process began slowly at first, but intensified over the years that followed as, gradually, all of the people — those loud, confident guys in expensive suits — were replaced by computers. These days we live in a world where machines make the trades, and where those same machines read our news stories and even our Twitter feeds, and react to what they see there in milliseconds, or even nanoseconds, faster than any human trader could even blink. A hoax tweet from a hacked Associated Press Twitter account, suggesting that President Barack Obama had been injured in an explosion at the White House, sent the stock market into almost instantaneous free fall, erasing some two hundred billion dollars from the market’s value. As soon as the tweet had been confirmed fake, the markets bounced back up again, just as quickly as they had gone down. The computers had made the costly mistake of believing Twitter and reacted as quickly as they had been programmed to do. These so-called Flash Crashes have become part and parcel of the modern stock market.

In his first month on the job, Nat had experienced the full, shocking enormity of a Flash Crash, and it had excited him like nothing he’d ever experienced before. May 6, 2010, had started out fairly normally for him, with the one difference that it was the day of the General Election in the UK, and that always made the European and US markets a little jittery. He had been looking forward to seeing how those nerves affected the market, but he hadn’t been prepared for what he experienced that day. Adding to the global tension on that day was the fact that, while the UK electorate had been casting their votes for a new government, the Greeks had taken to the streets to protest against the austerity measures being imposed by their own government. The mood on the market was already darkening by the time Nat had arrived at work, and every time Athens appeared on a news bulletin, another few points drifted away from the Dow Jones Industrial Average like wisps of smoke from a bonfire.

Suddenly, and without warning, what had started as a flutter in a reliable market became a shudder, and then a jolt as it spread to other stock markets and exchanges, immediately causing indices to plummet. Within seconds the Dow had lost one hundred points, and before finance workers could even begin to react, it had lost another hundred. And another. Brokers desperately tried to pull their stocks, cancelling orders in an urgent bid to limit the damage. Terrified, they huddled in communal spaces and watched the prices descend with unstoppable force. Seconds later, at six hundred down, the Dow had lost more than it had on the day that Lehman Brothers collapsed. Around him, traders were looking nauseous — it was like staring into the abyss. Even 9/11 hadn’t caused this much of a reaction, which suggested that something enormous had happened. But what? There was nothing on the news, nothing online. Why wasn’t someone stepping in and doing something to stop this madness? It was at that moment Nat realised there was no one who could stop this. It was already 2:.47 p.m. in the US, and the circuit breakers designed to halt trading following unusual price swings only worked until 2:30 p.m. They were on their own. The Dow was racing to a one-thousand-point drop, representing losses of around one trillion dollars, and it was sucking everything down in its path.

Then, out of nowhere, the market turned again and began to rise, almost as quickly as it had just fallen. Back to a mere six hundred down, then three hundred. Traders around the world let out a collective breath. The whole crash, the most dramatic in stock market history, had happened within ten minutes, and it was the most terrifying and exhilarating ten minutes of Nat Marley’s life. He had just witnessed the power of high-frequency trading and the algorithms which back the practice up, and he knew it was where he needed to be. He had seen into a trading world few outsiders could imagine: a global matrix of complex algorithms, running on interconnected computer nerve centres literally the size of houses, which fed seemingly omnipotent, supersonic trading robots governed by the very latest artificial intelligence. He was hooked.

Five years on, Nat had come close to achieving his dream of becoming one of the alpha males in this new world, and he had the respect of both his peers and his bosses to prove it. He was a data wizard, so skilled in spotting and predicting patterns in the market that he had risen to the top of his firm, and had even been moved inside their highly secretive quantitative derivatives operation. So, he was a quant — a mathematician who used quantitative techniques to predict markets — but he was better than most. Something about his attention to detail, or his ability to spot changes in the minutiae, made him sharper, faster, and far better than his peers. The piece of software he had built, that he had considered sharing with his current firm, was going to take him to the next level. He was almost certain his contacts would attack at some point, and he would be ready for them when they did. If his firm was running his program, they would be protected. That made him the most valuable asset on the market. And now here he was, outside the London headquarters of his dream firm, about to head up to a secret meeting with the man who could seal his place at the top of the tree. He felt totally pumped.

Nat fished in his pocket and pulled out the employee swipe card he had been sent in the mail, along with the invite to be here tonight. He had stuck to the orders contained in the message, and not even hinted to any of his friends and colleagues that he was being headhunted. He was quite looking forward to seeing their faces when he told them he was going to Eisenberg, Katz & Frey.

Not for the first time since getting the invitation, he wondered how he had come to their attention. Had somebody vouched for him? He couldn’t think who would have. He was exceptionally good at his job, he knew that, but it wasn’t the kind of industry where people supported talent anonymously. However it had happened, it was his turn now, and he wasn’t going to be shy about showing off his talents during this meeting.

Nat walked down the wide alleyway, around the west of the building to the side entrance, exactly as he had been told to do, and pressed the card against the reader. The light on the reader flicked from red to green, and he pushed the door open with his foot. Inside, the lights detected his movement and flickered on. It all felt very cloak and dagger, creeping into a competitor’s building late at night, to have a clandestine meeting about switching sides. He felt like a spy, and he realised that he liked the feeling. The door closed behind him with a heavy clunk and he followed the stairs up to the second floor, where he pushed out into the corridor, still following the instructions which had accompanied the invitation and the blank staff pass. He was moving slowly, taking his time. He had left the pub deliberately early to give himself that luxury. His father had always taught him that the greatest courtesy you could pay was to arrive on time, and as an adult he had made it a policy to always arrive exactly at the time agreed. Not before, and not after. He still had five full minutes to get to the twentieth floor before he was due to be there.

He slipped into the gents toilets on the second floor, just near the elevator he would be using. He wanted to make sure he looked his best. He leaned over the basins and stared at himself in the mirror. He was a good-looking guy, he knew that, and he was looking particularly good at the moment. He’d bulked up a little in the last year, spending more time in the gym and less time in the bar, and he was in a crisp white shirt that clung to his chest and biceps. He ran his hands under the tap and damped his hair a little in order to tame it back into its neat shape. He slid his jacket on and brushed both shoulders a couple of times. He looked good. He was the man. He was going to do this. This was his time.

He smiled at his reflection as he ran his hands under the dryer. Somebody had left a motorcycle helmet beside the basins. It struck him as odd that you would leave something like that behind. His invitation had implied that the building would be virtually empty. The financial software industry was a small one, and he really didn’t want to bump into anyone he knew before he was ready to break the big news. There was no sign of anyone in any of the cubicles though, so he shrugged and left the bathroom before the owner came back.

In the elevator on the way up to the twentieth floor, he ran through possible responses to the questions they may ask him. He didn’t know how these things played out — was it an interview or a formality? Either way, he would nail it. He was ready. He thought of his parents, and how proud they would be when he told them. They had no concept of what he did, apart from that he was very good at it, and had already made lots of money from doing it. He had bought them a lovely big house out in the country, and he’d given each of them a new car and an account stuffed with spending money. It seemed to make them happy, though happiness was not an emotion that came naturally to either of his parents. He’d bought his older sister a flat in the middle of the city, for which she had still to thank him. She had no idea how lucky she was to have him as a brother.

Once he was partner here, they would never want for anything again, any of them. His family was the only thing, apart from himself, that he cared about. He didn’t get to see them often, but he made sure they had everything they could possibly want.

A ping from the elevator doors told him he was on the twentieth floor. He set his shoulders as the doors opened. The entire floor was in darkness, with just the light from the elevator spilling out into the open-plan space. He wasn’t sure what he had expected, but he found it quite eerie that there seemed to be no one up here. He peered out, feeling a rising sense of trepidation. Had he got the wrong time? The wrong floor? Had he messed it up? Only as he stepped out into the darkness did he notice a solitary light coming from one of the corner offices. He breathed a sigh of relief and began walking towards it. Detecting his movement, the overhead lights flickered on up here too, and he blinked as soft fluorescent light flooded the room.

The twentieth floor was as spectacular as he’d always heard it was — a huge space, stylishly decorated and open-plan all the way round, with clusters of reassuringly over-priced desks concealed by designer screens. Metal, wood, glass — the modern style screamed sophisticated professionalism. The floor-to-ceiling windows gave a view out over most of London. The neon glow of the city bounced back up at him, flaring in multi-coloured starbursts in the rain on the huge expanse of glass. He smiled as he strode towards the corner office, he loved this place already.

When he got there, the office was empty. A laptop sat open and alone on the desk, lit by a neat desk lamp. A single chair had been pushed out from the desk in front of the laptop, as though the user had just stepped away briefly. The name plate on the door confirmed he was in the right place: Colm Monroe had sent him the invitation to be here tonight. The CEO of Eisenberg, Katz & Frey was renowned throughout the industry for hand-selecting each of their new recruits above a certain level.

Nat had been only slightly surprised to receive the invitation for a meeting, but he hadn’t been at all surprised by the clandestine nature of the arrangement. People in Nat’s position held a lot of information about their companies, and being seen even talking to a competitor was considered a betrayal of company policy. Nat was keen to find out what Monroe would put on the table, but he wasn’t about to throw his career away for a first meeting. After all, he had more to offer them right now, than they had to offer him.

Nat stepped in to the office and looked around. It was the kind of corner office you see in the movies: neat and ordered, with no over-flowing in-trays, empty coffee mugs or dying pot plants. A single photo frame on the desk showed just enough deference to a private life, but otherwise it was pure, cold professionalism. He liked it, it was the kind of thing he could see himself having one day. He stood in the doorway to the office, hesitating. Should he go in, uninvited? Or would he be better to slip away and come back in a moment, when Monroe was back at his desk?

No, he thought, this must be a test. He had arrived exactly on time and the guy wasn’t there, so this must be a little mind game, to see how he would react. He would go on in, he decided, and wait as though it was perfectly normal. But, before he could step inside, he heard a movement behind him.

“So you made it then?”

Nat turned around to find a short, broad-shouldered man standing very close behind him. He was smiling, but it wasn’t the warmest smile Nat had ever seen. In fact, it made him look quite sinister. He didn’t look at all like Nat had been expecting the great Colm Monroe to look. He had the same close-shaved head and dark eyebrows that Nat had seen when he’d looked the man up, but he had definitely been expecting him to be taller. His fearsome reputation seemed to demand a taller man.

“Was there ever any doubt?” Nat tried to make the question sound affable and relaxed, like he was one of the grown-ups. His heart was pounding in his chest. Monroe held his ground for a moment too long, not moving around Nat, and forcing him into an awkward side step as if to welcome the man into his own office. Monroe reached out his hand and shook Nat’s firmly, reaching his index finger up Nat’s wrist. It was an old trick which stopped the other person being able to exert any force in their own grip. Nat squeezed nonetheless — a limp handshake would be the kiss of death with a guy like Monroe. He felt the man’s nail scratch his wrist as he broke the grip and stepped past him, still smiling under lowered brows.

“So,” Monroe said, as he sat down behind his desk. “You think you stand a chance at Eisenberg, Katz & Frey, do you?”

He noticed an American lilt to Monroe’s accent. Was he putting it on for effect, or was Nat confusing his famous Scottish brogue for a Yankee drawl? Nat sat down calmly opposite Monroe before answering. He was determined to play this thing right.

“I’m guessing you must be thinking something similar, or we wouldn’t be here right now,” he replied. Was that too cocky for an opening line? Tough. He couldn’t take it back now.

“Fair point,” said Monroe.

His voice was more nasal than Nat had been expecting, too. He had listened to recordings of some of Monroe’s more legendary presentations, and the man hadn’t sounded so whiny.

“So,” Monroe continued. “Tell me about Flintlock and Staines.”

“What do you want to know?”

“They’re one of the best firms in London. Their turnover is in the billions. They only hire in the top five percent, and you’re sitting here with their biggest rivals. So why are you so keen to leave?”

Nat had prepared himself for this line of questioning. Loyalty to the firm was a prerequisite in this industry.

“It’s a fantastic firm, and I have been very happy there. But I’ve outgrown them, and let’s face it, it’s not Eisenberg, Katz & Frey,” Nat said. “Besides, I’m in the top two percent. Which is where you hire from. This is where I belong.”

Monroe raised an eyebrow. Nat was trying to read the expression. He had done his research — he knew that Monroe liked confidence and assuredness. He was legendary for finding the smallest hint of vulnerability and using it to rip young pretenders apart. If he liked you, you were in, but if he turned you down, the door was closed, and there was no way you would ever open it again.

“Relax kid,” said Monroe. “You’re not here to pitch. You’re here for your last chance.” Monroe pulled a pair of latex gloves from his pocket and began easing them onto his hands. It seemed a strange thing to do, but Nat had heard of people who were extremely anxious about touching surfaces — perhaps this was another one of Monroe’s legendary idiosyncrasies. With the gloves on, Monroe turned the laptop around to face Nat.

“Here,” he said.

Nat peered at the screen in front of him, and frowned. It was blank. A console screen. A cursor blinked, awaiting instructions.

“You remember how to access your own server, right?” Monroe leered over the top of the laptop screen.

“Of course, but what—?”

He had been expecting a tough interview, but he had no idea what was happening here. Monroe sighed and looked at him, waiting for a realisation that obviously wasn’t going to come.

“For a genius, you’re not very bright, are you?” he said, coldly. “This is your last chance, son. Hand over the code.”

Nat felt sweat beading up on his face. What was happening? Why was Monroe behaving like this? Was he part of The Water Boys? Was he Shylock? Surely he couldn’t be involved with a group like that.

“I’m afraid you’ve got yourself into a very unpleasant situation, Nathaniel,” said Monroe. “I imagine you’re not feeling very well, right now.”

He was right, Nat was breathing heavily. He felt nervous, uncomfortable, jittery.

“What’s going on?” he asked, somewhat pathetically.

Nat could feel his heart fluttering. What was happening to him?

“You have been injected with an extremely fast-acting poison,” said Monroe. “I have an antidote, but you’re going to have to play ball.”

“I won’t do it,” Nat said, firmly.

Monroe just smiled.

“No skin off my nose,” he said. “Think how it will look when they find you here, in the competitors’ office, server compromised, covered in your own piss. How’s that for a legacy?” Monroe was absently wiping a clean handkerchief over the table’s surface, cleaning it while he spoke.

“You can’t do this,” Nat gurgled. He was struggling now. His lips weren’t responding to his brain, and he was finding it hard to swallow. He tried to keep the desperation from his voice, but he could feel his throat tightening. His skin was hot and clammy. He was beginning to panic.

“It’s already done, mate,” Monroe said. “It’s up to you now. You want it to stop?”

Nat leaned forward. His head was swimming. He took a deep breath, trying to steady himself. It didn’t work. He didn’t feel in control of his body any more.

“All you have to do is hand over the code, and I’ll make it stop,” said Monroe.

“Okay,” Nat said, with a thick tongue, not forming the word properly. He forced himself to lean closer to the computer, but his body felt heavy and outside of his control. Monroe pushed the machine closer to him and Nat tried to navigate to his own remote server. His fingers wouldn’t respond to his brain. Finally he managed to key the numbers in and hit return. The root of his private server popped up, requesting a username and password.

Nat looked at Monroe. The man looked cold, dispassionate, and stupid. He knew that Colm Monroe was not a stupid man, but the guy in front of him right now looked pretty dumb. He was leering at Nat, waiting for the code. Nat’s body may have felt like an alien vessel that no longer belonged to him, but his brain had just begun working with alarming clarity. This man was not Colm Monroe. He had been tricked. He had been stupid. He had fucked up. Defiantly, he decided that he would rather die than give them his code. It took all of his strength to push the laptop away. It was meant to be a big gesture, but in reality it moved less than an inch.

“No,” he said. It sounded more like “Nnn”. His tongue was fat and heavy in his mouth. His heart was thumping; he was feeling worse by the moment. He was short of breath, and his skin was clammy. He ran his finger around the inside of his collar, trying to loosen it, but it didn’t help. The world was closing in around him. He could feel his shirt sticking to his skin under his jacket and he felt like it was strangling him. He needed to get out, to get away from here. He stood up, shakily, feeling his legs wobble beneath his weight.

Monroe didn’t move to stop him, and as Nat tried to walk away, he saw why. He wasn’t going to make it. Nat managed to get within a yard of the door before his legs gave way. He turned back and tried to reach one of the sofas behind him, but he sank to his knees before he could get there. He was gasping for air now, and pulled at his tie to loosen it.

The man who wasn’t Colm Monroe made no move to help him, but just looked up over the laptop screen with a small frown.

“Oh God,” said Nat, gasping desperately for breath, but none would come. He lay down, hoping for some relief. He was choking, asphyxiating, dying. The reality hit Nat like a sledgehammer: he was going to die, and there was nothing he could do about it. His mind was working overtime, but his body had given up. The pain burning through him as his body shut down was unlike anything he had ever felt before, but he couldn’t get his strangled throat to make a sound. He was terrified, and he couldn’t force a single muscle to fight back. Nothing would help him. The last thing Nat saw was the man pretending to be Colm Monroe stand up from the laptop and turn away to face the window, as though he didn’t want to watch. Nat gave in to the darkness.