Maisie looked up as the morning post arrived in a flurry of wings. "It's here!" One owl, struggling beneath the weight of a long package, swooped over her and let its burden fall. Mike covered his porridge protectively, but Maisie caught the parcel before it hit the table.

"That had better not be a Beater's bat, Wilkins," Professor McGonagall said directly behind Mike, making him jump. I'm sure she was nowhere in sight a minute ago.

"No, Professor," Maisie said quickly. "That would be against the rules."

Colin inhaled a mouthful of pumpkin juice and started coughing. Mike pounded him on the back. The Headmistress regarded them all sternly, and then held out her hand. Meekly, Maisie handed over her parcel. With a flick of her wand, Professor McGonagall opened the brown paper wrapping and surveyed the contents. "Cricket?"

"Yes, Professor," Maisie said. "Mike and Colin have never played. I thought I'd teach them."

Professor McGonagall handed the parcel back. "Well away from the Greenhouses, please. And the castle. And anything else with windows."

"Yes, Professor," all three of them chorused.

"Well away from the castle," Colin muttered as Professor McGonagall strode away.

"We'll be well away from the castle windows, which is what she really meant," Maisie said. "Do we have enough potion left?"

Mike nodded. "For one more trip, so you'll have about forty-five minutes to hit it, accounting for time for us to get in and out safely."

"Easy," Maisie said.

It wasn't, quite. That evening, Colin and Mike stood, holding down the two levers, until Mike's hand was cramping, while Maisie tossed up the small red ball and swiped at it with the bat. She hit the walls, the ceiling, and once nearly Colin when the ball came rocketing back down, and cursed, and tried again.

Mike checked his watch. Half an hour … plus five minutes getting in here … "Maisie …"

"I've nearly got it," she said between her teeth, tried again, missed again, swore again.

"You need to be further away," Colin said unexpectedly.

Mike rolled his eyes. "It's not going to be easier for her to hit it from further away."

"The angle will be better. Maisie, you're trying to hit it almost straight up, which means you can't look where you're hitting it at the same time as you're swinging. Come over to the edge and try it at an angle."

"I think I know how to hit things," Maisie said shortly, looking rather as if she'd like to send the next ball straight at Colin.

Mike checked his watch again. Thirty five minutes … "Give it a try. It's not as if you're hitting the lever now, are you?"

"Fine." Maisie stomped over to the edge of the room, tossed the ball up, and swung.

And missed.

"It was closer though, I think," Colin said.

"Yes, it was," Maisie grudgingly admitted. "Mike, do you think you could toss the ball to me?"

Mike shifted his grip on the lever to his other hand, and worked his fingers. "I can try."

She trotted over to hand the ball to him. "Just throw it straight at me. Aim for my head, that will give me the right height."

Mike weighed the small, hard red ball in his hand, and shrugged. "Alright. It's your head."

They tried it that way a half-dozen times, with what Maisie claimed were increasingly closer misses. "You need to throw the ball harder, Mike."

"I'm throwing it as hard as I can!" he snapped.

"Try a spell," Colin said. "Isn't there one to throw things? Your magic's much stronger than your muscles, you know, Mike."

"I'll try." He dropped the ball to the floor and took out his wand. "But this is the last try, Maisie, or we'll start hiccoughing again on the way out."

"Well, you throw it properly, and I'll be able to hit it properly," she snapped.

Mike eyed her. Properly, eh? "Wingardium Leviosa!" The ball rose in the air. Now, I want force and propulsion … I can flick it with Levitation, but not fast enough … I wonder …? He took a deep breath and focused on his wand. "Waddiwasi!"

The ball shot across the room as if it were, in fact, a Bludger, heading straight for Maisie's head. She stepped forward as it came, bracing herself, and swung the bat in a great arc that hit the ball with a crack as loud as someone Apparating. The ball flew upwards, out of Mike's sight, struck something —

"Yes!" Maisie cried, capering on the spot.

From all around them, a hollow voice intoned, "The Quidditch Key, which Seekers seek, shall be found where the confused tear creaks. In darkest night, or dawn's mixed grey ink, the Key shall help you find the Snitch."

"What?" said Colin.

"Shhh!" Maisie hissed.

The three of them waited, straining their ears, but the voice said nothing more.

"It's a clue," Colin said. "Isn't it? It has to be. With the 'shall be found' bit."

Maisie's forehead wrinkled. "That doesn't make sense. I mean, I get hiding the Key somewhere like this, with a scary flaming sword lady to keep people out. But why make a clue to finding the Key and then make it so no-one will find the clue?"

Mike looked at his watch. Fifty five minutes. Oh, cripes. He let his lever go. "We've got to go," he said. "Like, now, Maisie."

They almost didn't make it. Maisie, bringing up the rear, was halfway down the corridor when she gave a sudden loud hiccough.

"Run!" Colin shouted, and all three of them pelted for the exit, diving through it and slamming the door on "WHO DARES DISTURB MY REST!"

Colin leaned back against the door, panting. "I'm really very glad we never have to do that again."

"We can't," Mike pointed out. "No more Solution to Hiccoughs." He peered up and down the corridor, but there was no sign of either Filch or Mrs Norris.

"The Quidditch Key, which Seekers seek," Maisie muttered to herself, "shall be found where the … tear leaks. In darkest night, or dawn's grey … light? The Key shall help you find the Snitch. The Quidditch Key, which Seekers seek … oh, why didn't I bring parchment and a quill?"

"I've got it," Colin said confidently, and when the other two stared at him, "What? I have. The Quidditch Key, which Seekers seek, shall be found where the confused tear creaks. In darkest night, or dawn's mixed grey ink, the Key shall help you find the Snitch." He shrugged. "Let's go downstairs, and I'll write it down for you both."

Maisie started towards the stairs. "Alright, then, but are you sure that's right? I mean, really sure? Because if you're not, Mike will have to ask Professor Granger's teaching assistant for another Cinderjuice lesson —"

"I am sure." Colin jumped the first trick step. "We don't need to got back, and Mike can't ask him, anyway. It's not safe."

Maisie hopped over the step and stopped, turning to frown up at Mike. "I thought you said he was fine. Just invisible."

"He was," Mike said. "He wasn't even really that sarcastic, not like he was when he was being Professor Granger. I don't mind, really, Colin."

"No," Colin said firmly. "You can't risk it, not now he might be a Death Eater."

Maisie stared at him. "What?"

Mike took a long, careful step down to join them. The Prefects might say no-one could actually fall all the way through the staircase, but this particular staircase was an awfully long way up to take the risk. "I thought you said that was just a joke."

Colin shook his head. "No, you said it was a joke, and I said it might be, but it's not worth taking the risk if it wasn't, is it?" He trotted a few steps down towards the landing, and then stopped when neither Mike nor Maisie followed him.

"Nobody jokes about being a Death Eater," Maisie said flatly. "One of you tell me what by Circe's socks you're talking about."

"We saw him," Colin explained. "Professor Granger's teaching assistant. Talking to Professor Potter and Professor Longbottom. They knew him, obviously."

"None of us has ever seen him," Maisie said. "How did you know it was him?"

Mike pushed her gently, and she took a couple of steps down the stairs. "I recognised his voice. So would you, if you'd heard it. He said something to Professor Potter about being a Death Eater, and Professor Potter said he'd been in the Order of the Phoenix too." He shrugged. "Either he was joking, or he was a spy. Either way, he's not dangerous. Professor Potter and Professor Longbottom were talking to him perfectly normally."

"That's true," Colin admitted. "And I suppose if they know he's here, he can't be a real Death Eater, can he? No-one would let one of them anywhere near the students."

"Maybe he Imperiused them," Maisie said darkly, stopping again on the landing. "They used to do that, you know, a lot."

Mike frowned. That's the curse she mentioned in the Forbidden Forest. "I still don't know what that is, Imperius."

Maisie peered down the nearest corridor, and then over the balustrade, before answering. "It's a curse, an Unforgivable curse. Using it gets you a life-sentence in Azkaban. It makes someone do anything you want them to. Kill themselves, or kill someone else, or give you all their money, or anything."

"Let a Death Eater into Hogwarts and treat them like they're a normal person?" Colin asked, his voice echoing the slowly dawning horror was creeping along Mike's nerves. Maisie nodded grimly. "We have to tell someone! Professor Granger, or the Headmistress, or someone!"

"Wait," Mike said. Professor Potter … and Professor Longbottom … and who else? "What if they're Imperiused too? What if they're Imperiused to expel any student who finds out?"

"A Death Eater wouldn't do that," Maisie said. "He'd make them kill any student who found out. That's what they're like."

Mike frowned. "How come you know so much about them?"

"Because …" Maisie took a deep breath. "My cousin Ella was a sympathiser. You all saw my Boggart, that night in the forest."

"I saw a spider," Mike said. "And a Death Eater, but that was mine, I think. And something else, but I was a bit distracted at the time."

"It's the Dark Mark," Maisie said. "My Boggart is the Dark Mark. My parents told her she wasn't to ever come to our house again, and that night, the Death Eaters came for them. We only just got away. If the Death Eaters would kill people just for being inhospitable, what do you think one would do to protect himself?"

"Then what do we do?" Colin asked. "We have to do something! We have to tell someone!"

"You don't get it, Colin!" Maisie snapped. "You can't trust anyone! We can't trust each other! He could get any of us alone —"

"He did get me alone." Mike's stomach churned and cold sweat prickled on his skin. They can make you do anything … anything they want you to do. "Do you think he did that to me?"

Maisie sighed. "No. Not really. Because one of the things he'd want you to do is tell him straight away if anyone guessed who he was, and you haven't told him you and Colin have, have you?"

"No," Mike said. He wiped his palms on his robe. "No, I didn't."

"Unless you're lying about that," Colin pointed out. "Which he'd want you to do."

"Now do you see why it's an Unforgivable?" Maisie said.

"He must be a really powerful wizard, to be able to Imperius someone like Professor Potter," Colin said, sounding like he was on the verge of tears. "He's an Auror. He's the Auror. Even Voldemort's killing curse just bounced straight off him."

"We should just leave." Mike said. "Like, right now, tonight. Run away. Go home." Except they'd catch us straight away, as soon as they knew we were gone … he'dcatch us straight away …

"We can't," Maisie said. "Not and leave everybody here, with a Death Eater roaming around."

"And what are we supposed to do about him?" Colin demanded. "Throw our homework at him? Hit him with a Tarantallegra?"

"My Protego is getting pretty good," Mike said slowly.

"Are you completely bloody mad?" Colin's voice grew shrill. "You're eleven! I'm eleven! Maisie's eleven! I don't care how much you've been practising, he's a grown-up and a Death Eater and —"

Maisie put her hand over his mouth. "Just breathe in and out," she said. "And shout a bit less. Don't forget, Mike said he could turn himself invisible. He could be anywhere."

They all looked around at the same moment, staring into the shadowy corridor and down the stairs.

Invisible Death Eaters. Who can make anyone do anything they decide they want them to do. Mike's teeth wanted to chatter and he clenched them together. He didn't think he'd been Imperiused. But how would he know? Would he feel different? Would he even remember? There was a spell that could do that, he'd read about it. Oblivion, or Obliterate, or something.

Oh, Merlin's mercy, I could be under his control right at this second and not know it, and be about to push Maisie and Colin over the banister.

He took out his wand, nearly dropping it as his sweaty fingers fumbled the grip, and held it out to Maisie. "You'd better take this. Until we know I'm alright."

She took it gingerly. "I'll ask Professor Potter in class tomorrow, if there's a way to tell if someone's Imperiused."

"But if he's —" Colin said.

Maisie cut him off. "I'm a student, it's not suspicious for me to be curious. I'll say I was reading something about the War."

"Well, that's fine," Colin said. He looked around again and lowered his voice to a whisper. "But what are we going to do?"

Maisie lifted her chin. "We have to stop him, that's all."

"That's —"

"Completely mad, yes, I know, Colin! But we can't just pretend we don't know, can we?"

"No," Colin admitted. "We can owl the Ministry."

"Dear Minister Shacklebolt, I am eleven, one of my teachers is a Death Eater," Mike said.

"Owl him anonymously. Or send an anonymous tip to The Prophet, or The Quibbler."

"The Quibbler would be better," Maisie said. "They publish anything."

Colin snorted. "So does The Prophet, they had one story about Severus Snape abducting people in a flying saucer."

Mike's forehead wrinkled. "With an extension charm? Because otherwise —"

"A space-ship, Mike, not Spode!" Maisie snapped. "And I don't care about Severus Snape, I care about the Death Eater in Hogwarts! We have to find out why he's here."

"The Key," Mike said. "You said it, Colin, that day he taught us as Professor Granger, remember? That he was here to steal the Key? I bet that's why Professor Granger and the others are looking for it — because he's making them!"

"I said that before I knew he was a Death Eater. Why would a Death Eater care about Quidditch? I mean, do they have a team? The Death Eater Dervishes, top of the league? No."

"Money," Maisie said suddenly. "People bet huge amounts on the matches. If you could control the outcome … he must have been on the run for five years, to be free and not in Azkaban. I bet he's desperate for enough money to get out of the country and hide himself somewhere."

"If we find it, and give it to him, then he'll leave, won't he?" Colin said.

"Probably killing everyone on the way out the door," Maisie said.

"Try to be a little bit constructive, Maisie," Colin snapped. "Is there any way to tell if someone is under this Unforgettable curse?"

"Unforgivable," Maisie corrected. "And no. That's why so many Death Eaters got away with it, the first time. They said they'd been Imperiused and no-one could prove they hadn't been."

"Does it wear off?"

"Usually it has to be lifted, or the caster die. Unless it's a feeble version."

"None of that is helpful," Mike said.

Maisie took a deep breath, and closed her eyes for a moment. "The first thing we have to do is make sure he doesn't find the Key."

"The first thing we have to do is work out how to raise the alarm!" Colin said.

She shook her head. "No, that's the second thing we need to do. As long as he's here, looking for the Key, he won't hurt anyone. He can't, can he, without people realising something's really wrong? Even if there are some teachers under his control, they can't all be. Or all the students. So long as he has something to lose, he's safe."

"Safe," Colin repeated flatly.

"Safe-ish," Maisie corrected herself. "But what if we're in the middle of trying to persuade our parents that we're not candidates for the Janus Thickey ward, that there really is a Death Eater in Hogwarts, and he finds the Key? He'll kill everyone who's seen him, disappear, and never be seen again. We have to get the Key, and we have to keep it safe, to buy time." She looked from one to the other. "We have to pretend nothing's wrong, too. He mustn't realise we know, or else we're all in danger."

Colin and Mike nodded solemnly.

"Right." Maisie took a deep breath. "So the very first thing we need to do, after we make sure Mike isn't, you know …"

"His magical slave," Colin said, which Mike could have done without.

Maisie nodded. "The first thing after that is work out that clue."

.

.

.

Author's note: Waddiwasi, the spell Lupin uses to send a wad of chewing gum up Peeves's nose, is probably not powerful enough to move a cricket ball, but I took artistic licence.

Well, that escalated quickly … how many ways can this go wrong?