It couldn't be Raj Patel, or Sylvain, Carter or ...

Her thoughts always ended in the same place: it was impossible to imagine anyone she knew in Night School betraying Isabelle and the students like that.

But somebody was.

When she wasn't running on the school grounds, studying or learning defensive techniques, she was trying to convince Zoe to like her. But all her efforts backfired. The harder she tried, the more suspicious the younger girl was of her motives.

Zoe's strange, emotionless way of talking and her almost mechanical approach to work and problem-solving made her hard to like. It had taken Allie a while to truly accept that behind the wireless robot facade and almost scary intelligence was a thirteen-year-old girl.

Zoe hated small talk. Allie's attempts to engage her in chitchat always ended with Zoe staring at her with blank fierceness, as if she were trying to figure out what it was about Allie that was so annoying.

One day when Allie was talking about their science assignment, Zoe interrupted her mid-sentence.

'You talk too much,' she said. Then she got up and walked away, leaving Allie staring after her, open-mouthed.

But when they were training, Zoe was a good partner. Whenever Allie quickly learned a move, Zoe would try to compliment her, although it usually came out as, 'You learned that quicker than usual. What's wrong?'

But there was something vulnerable about Zoe that made Allie keep trying.

'She's kind of like a pet ... person,' she'd told Rachel.

Rachel smirked. 'I wouldn't let her hear you say that.'

'Like a cobra-kitten hybrid,' Allie continued, undaunted. 'Cute and vicious at the same time.'

'Or a python-puppy,' Rachel offered. 'But if you tell her I said that I'll call you liar to your face.'

'I wouldn't dare.' Allie shivered. 'She'd hurt me.'

By the time Jerry Cole assigned them to practise surveillance techniques on an unseasonably warm afternoon in October, Allie had begun to believe she'd never win Zoe over. As the two struck out after their surveillance subject, Allie kept saying in dramatic tones, 'It's Night School by day ... day ... day', adding an echo effect to the last word as Zoe glowered at her threateningly.

Their assignment was to follow a Night School student named Philip for three hours without being discovered. They had to track his every movement and record them on a form.

When they got their assignment, they both thought it sounded kind of cool.

It was unbelievably boring.

First Philip spent an hour in the library studying alone. Then he went into the boys' toilets. For ages.

They were in the hallway arguing about whether or not to go in and check on him when he emerged so suddenly he almost ran into them. Luckily, he seemed distracted and hurried outside without noticing them. Upon following, they watched as he joined a group of friends playing football.

While he played, Zoe and Allie hid in the woods, spying on him through the trees.

'He's intercepting the ball!' Zoe announced, watching Philip through a shield of bracken. 'Oh no. He's missed again.' Turning to face Allie, she sat with her back to the game. 'He's rubbish.'

Holding a thick leaf of grass between her thumbs, Allie blew on it until it made a squawky trumpet sound. When she tired of the noise, she let the grass float from her hand.

'God, this is dull. Why couldn't he do something interesting? Like get in a fight or ... anything that isn't this?'

Eventually, they decided to play games to pass the time. First I Spy then, when that grew dull, Cloud Animals.

'I see a minotaur,' Zoe said, as they lay on their backs staring up at the sunlit blue sky.

'No you don't.' Allie, who saw nothing but shapeless blobs, leaned over to squint at the cloud Zoe pointed at. 'That's nothing.'

'It's a minotaur!' Zoe insisted. 'Look. Two horns there, and a freakishly muscled torso there. And a kind of tail thing. It's a minotaur.'

'Minotaur,' Allie mumbled to herself. 'Well, I see a duck.'

'Really?' Zoe looked where Allie pointed. 'I don't think that looks like a duck. Looks more like a rabbit.'

'Fine,' Allie sighed. 'Then it's a rabbit-duck. A dabbit. Or a ruck.'

A bird fluttered from the trees to the ground nearby, cocking its head at them before changing its mind and flapping away. Allie barely noticed it out of the corner of her eye as she looked for a more interesting cloud to challenge Zoe's minotaur.

'Oh no,' Zoe whispered to herself. 'Just one.'

Allie was still staring at the clouds. 'Yes. Just one dabbit, Zoe.'

But Zoe wasn't talking about dabbits any more. She leapt to her feet and stared up at the trees, panic-stricken. Allie squinted to see her against the bright sky.

'One for sorrow; there can't be just one. There must be two. One for sorrow, Allie.' Zoe's voice was urgent as she turned back to look at her. 'Help me find another!'

'Find another what?' Startled, Allie scrambled to follow her but the younger girl had already run into the woods. When she found her a few seconds later, Zoe stood in a clearing, her eyes roaming from tree to tree. 'Find another what, Zoe?'

The younger girl pointed up, to where the fat, glossy magpie balanced on the branch above her head, its tuxedo colouring strangely out of place. It darted a look down at them before something else caught its eye.

'There can't be just one,' Zoe was muttering to herself. 'There can't be just one.'

Still confused about where all this had come from, Allie scanned the surrounding woods for a bird any bird. 'There.' She pointed across the treetops to a tall horse chestnut tree far away where one could just be seen on the highest branches, swaying in the light breeze. From here there was no way to tell what kind of bird it was but she hoped it would look like a magpie to Zoe. 'Isn't that a magpie?'

Doubtful, Zoe stood on her toes, peering into the distance. Then she gave a squeal of happiness and clapped her hands.

'Yes! Two for joy!'

Startled, the first magpie flew away.

Without another word, Zoe ran back to where they'd been playing Cloud Animals earlier and lay down again, looking up at the sky as if nothing had happened.

After a second, Allie sat beside her, a puzzled frown creasing her forehead. 'So,' she said carefully, 'magpies?'

Frowning, Zoe scanned the clouds. 'There can't be just one, Allie. Ever.'

'Because of the poem?'

Zoe nodded.

Allie remembered it vaguely. Her mother had sometimes recited it if a single magpie crossed their path. One for sorrow, two for joy, three for a girl, four for a boy ...

She knew some people were superstitious about the birds, or considered them to be bad luck, but she'd never seen anyone react like Zoe. As she considered this, Allie glanced absently towards the football players but the lawn was empty. They'd gone.

'Oh balls, Zoe, we've lost sodding Philip.'

But it didn't matter that they lost him and got marked down for it, or that Jerry looked at them with disappointment. Because somehow that afternoon changed everything.

From that day on Zoe accepted Allie completely.

The spate of warm weather didn't last and the sound of rain lashing against the windows accompanied Allie a few days later as she walked with Carter down the stone stairs to the basement training room talking about what had happened the night before. The weather had been fierce then, too. So instead of going for a run they'd been given a word problem to work out. Written in Eloise's neat, square handwriting on a white board, it had confounded them all.

A runaway train, packed with passengers is about to crash. You can save all the passengers by switching the train to another track, but if you do that, one innocent person will die. Is it right to sacrifice one to save the lives of many?

As usual, all they'd been told was that this was the sort of decision they might have to make some day, and that there was no right answer and no wrong answer. Instead, they were to make their own decisions.

It drove Allie crazy.

'It's horrible. I mean, what kind of question is that?' she said now, as they walked under the flickering fluorescent lights of the basement hallway. The air smelled musty; it felt cool and damp against her skin. 'And how can they not tell us what right is?' She shook her fist at the ceiling. 'I need to know what right is!'

'You'll get used to it,' Carter said. 'They're always asking us things like that.'

'What are they trying to teach us?' Allie asked. 'How to be evil?'

'Maybe.'

Allie watched him out of the corner of her eye as his expression clouded. She didn't say anything but she was glad he wasn't always OK with the things Night School demanded of them. That he could look at it all and wonder, as she did, Is this fine? Or is this really not fine at all?

'Well, it won't work. We're too nice for them. They will never succeed.' She pushed open the door to Training Room One. 'They'll learn ...' But as she looked inside she lost her train of thought. The blue mats were gone. A table stood at one end of the room, faced by metal folding chairs arranged in rows.

Looking over her shoulder, Carter murmured, 'What the hell ...?'

Exchanging a worried look, they walked in together, slipping into two free seats.

'What's going on?' Allie whispered, but Carter shook his head. He didn't know either. Worry chilled Allie like a cool breeze. The room had the ambience of a church sanctuary before the sermon began everyone sat in poses of subdued reverence. She got the feeling nobody knew what was happening, but they all knew it wouldn't be good.

By the time the doors swung open ten minutes later the air fairly crackled with tension. The Night School leaders walked in together like they were heading into battle Eloise, Isabelle, Zelazny, Jerry and Raj, all dressed in black and matching each other stride for stride. They didn't look at the students until they'd taken their seats at the front of the room, then their eyes swept the room impassively.

Allie twisted the edge of her shirt around one finger so tightly it cut off the blood flow.

Raj spoke first. 'What you're going to do this week isn't easy, but it is critical. Each of you will be assigned one person to interview. You are to ask your subject about every aspect of their life and produce a written report. In that report you will decide whether or not the person you investigate is telling the truth. Throughout the week you will each receive one-to-one training in lie detection. By the end of the week we expect you to be able to identify all the signs of falseness vocal tics, mannerisms, tells. You will use those to determine the truth.'

He leaned back, and Eloise took over. 'Assigned subjects will, in many cases, be someone you already know in fact, somebody you know well.' A dismayed murmur crept through the room. 'Through this you will learn how to separate your emotions from your work. However, you should know that your subject will never see the report you write for us. This will be completely confidential and should, therefore, be the unvarnished truth.'

Placing her palms flat on the table, she emphasised the next words. 'Lying to your interviewer is grounds for expulsion from Night School and Cimmeria Academy.'

As Zelazny took over, Allie felt herself move back in her chair, as if to get further away from them all.

'Subject assignments are secret only you and your subject should know you are investigating them. Do not reveal these to anybody else.' His icy eyes surveyed them. 'Anyone found to have revealed this information will be punished.' Reaching into a briefcase on the floor beside him, he pulled out a stack of thin black folders. 'When your name is called, please come forward to collect your assignment. Anderson ...'

As a tall, slim girl walked to the front of the room for her folder, Allie and Carter exchanged a quick despairing look.

While the stack of folders dwindled in front of Zelazny, Allie watched as first Lucas then Jules collected their assignments.

When Zelazny called out, 'Glass!' Zoe strode past them, visibly fuming. She snatched the folder from his hands. 'This is lame,' she muttered as she passed Allie on her way back to her seat.

Finally, Zelazny barked, 'Sheridan!'

Taking a steadying breath, she walked to the front of the room. She kept her face blank although her hands curled into fists at her sides. She made herself meet Zelazny's frigid eyes as she took the cool folder from his hands. The entire process of walking from her seat to the table and back again must have taken less than a minute. It felt endless.

Carter's was the last name called. As he stood up he gave Allie a helpless look.

'You now have your assignments.' Isabelle's cool, clear voice rang out after he returned to his seat. 'Your absolute discretion is required with this process.'

While she spoke, Jerry took off his wire-framed glasses and wiped them with a cloth. When finished, he took over for the final part. 'Spend time with your subject. Learn to ask the right questions. And to tell truth from a lie. This is important.' Replacing his glasses on his nose, he studied them all solemnly. 'Somebody in this room is working for Nathaniel. Lying to all of us. You could find that person. The process starts tomorrow. There will be no Night School training this week we want you to focus solely on this project.'

As the students shuffled out of the room, Allie and Carter caught up with Lucas and Jules.

'Can you believe this?' Lucas looked disgusted.

Shaking her head, Jules glanced up at Carter. 'I don't like this at all.'

Her worried expression made Allie nervous.

Nothing ever bothers Jules.

'This isn't going to end well. Someone's gonna get their feelings hurt,' Lucas joked darkly, trying to lighten the mood. 'And I'll bet it's me.'

But nobody laughed.

Back in her room later, Allie sat on her bed, the folder closed in front of her; a rectangular black hole amid the milky whiteness of the duvet.

Nobody had wanted to hang out. By unspoken consensus they'd all parted at the top of the stairs, everyone going their own way.

Now she knew she had to open the folder and see whose privacy she was going to invade. Whose honesty she was about to doubt. And who would probably hate her before the week was over.

Eloise had said the assigned person would be somebody they knew well.

A horrible sixth sense told her she already knew what she would find inside that folder. Still she looked at it for a long moment, her hands refusing to move.

Finally, closing her eyes, she reached out blindly for the folder. She could feel the cool smoothness of the cover beneath her fingertips, then the sharp ridge of the edges. She flipped it open.

Saying a silent prayer, she opened her eyes.

Two words stared up at her, written in neat black letters against the white background of the page.

'Carter West.'