The next thing Draco knows, he's locked in the library, and Potter is banging on the door.

"Let us out of here you prats!"

Draco turns away. Granger is quite frightening when she wants to be. And it's Potter who's still fixated on their conversation last night, not him. Even if Potter can't be civil for a few hours, they'll be let out eventually.

Hopefully.

Granger threw a tin of biscuits from Weasleys' Wizard Wheezes at them on their way in, which implies she doesn't plan to let them out any time soon.

Draco scans the shelves farthest to the left while Potter looks opposite. It's not lost on him that, eventually, they'll meet in the middle.

He breezes past the sections on Arithmancy and Astrology, stopping only briefly to pull Aquatic Wonders of Yorkshire: A Wizard's Field Guide and Bestiarium Magicum from their housing under Biology before moving onto Herbology.

Despite what Granger ordered, he thinks he's got a better shot of solving this if he's reading up on related subjects, rather than fictional stories.

He unshelves Magical Water Plants of the Highland Lochs and Winogrand's Wondrous Water Plants next, then focuses on the Charms and Spells section.

A Compendium of Common Curses and Their Counter-Actions might be useful, as well as the Updated Counter-Curse Handbook ... Draco stops at a text on bezoars.

Could that be of any help? Traditionally, bezoars only work for potions, but maybe there's a way the bezoars can be prepared that would stop spell effects too.

Then again, there's no way the Wallygagglers can raise enough goats to slaughter one every time a member of their pod gets hexed. Maybe Draco can cultivate some sort of herb that will have a similar effect...

He'll have to speak to Luna about it.

Potter's voice calls his attention from the other side of the room. "I don't know what I'm doing here."

Draco looks up, then looks away. "Granger—"

"I don't mean that." His words come out roughly, but then he softens. "I mean I've never given a damn about interfering with magical creature livelihood before. If I'd shown even the slightest interest, Hermione would've kept hounding me to join S.P.E.W. But I'm here."

"Right."

Draco doesn't add anything else.

"What I'm trying to say is that ... maybe that was a mistake, a small one, to decide to do this, but maybe it's still worth it. To be here."

A laugh cuts its way out of Draco's throat. "Okay. Does that mean you're selfish too?"

"I think my life has been unique enough that I get to pretend you don't have anything in common with me, thanks."

"Go ahead. I won't stop you."

"Much appreciated."

Draco can feel the edges of his mouth fighting a smile, and he just lets it go.

Potter is so ... he's so much, all the time. Draco doesn't know what to do with all of it. How do you make someone understand something about themselves they're hiding from? Harry Potter is everything in the world dialled up to a thousand. His magic, his emotions, everything.

Draco can't keep ignoring that, trying to pretend Harry hasn't already cracked every barrier he put in place, just by existing.

Harry tries to tamp everything about himself down, but it'll just keep getting bigger. Draco wonders how so much of a person could have ever fit in something so small as a cupboard under the stairs.

"I had some bad reactions a few years after the war," Harry says. "Mostly when someone would get rid of something without warning. Hermione Vanished a takeaway container once, and I just..." Harry sighs.

"If you think my reaction to learning that you're human would be judgement, you're wrong."

Harry sucks in a breath. He shuts the tome he's reading with a gentle, "Oh."

"At the auction ... What was that about?" Draco asks, because he's been wondering, and because he's not sure he'll get another chance to.

"You mentioned that Hermione was redecorating her office. I knew that meant she was getting rid of some stuff, and I just felt ... out of control." He shakes his head. "It's not her fault. She should get to make her own decisions without worrying about me. But knowing that doesn't mean I'm any better at..."

Draco nods.

They're only a metre or two away now. Harry must have been moving faster than him, not taking nearly so much time scanning over the titles, because they're only at F, fiction, which is certainly not the centre of the alphabet.

Harry grabs for the boxed set of The Wandering Wallygagglers of North Moor and adds it to his stack.

Draco pulls a novel called Wacky Wallygaggler Wally's Adventures in the Non-Magical World. Thrilling.

They reach for Wallygaggler Thieves and Other Exciting Bedtime Stories at the same moment, and Draco pretends not to notice that their hands brush, adding it to his stack when Harry's twitches away.

They gather all their books and move to the armchairs. Harry starts a fire so they have better light to read by, and because it's grown rather cold. It's still raining outside, but now it has slowed to a steady thrum.

Draco begins at the top of his pile of books, poring through them with a concentration that Harry is trying his best to rival — though, if his tapping feet are any indication, he's not doing a good job.

It's a few hours later, judging by the way the winter sky outside the window has faded to the bruised purple of a plum, when he begins to feel peckish, and gestures wordlessly for Harry to pass him the biscuit tin he's tearing through.

He finally selects a Ginger Newt with an appropriate amount of apprehension, considering that the source of these was a joke shop. Ginger Newts are always safe. And besides, Harry has eaten nearly half the tin now, and he seems fine.

When all is still normal a few moments later, he goes back to reading. Until, that is, Harry interrupts.

"Do you reckon we'll actually find anything useful in these? I mean, half of what we grabbed, they're children's stories." A smattering of crumbs falls from his lips to his shirt as he speaks. Harry seems surprised to notice this, and he brushes them off with an absent hand.

"The Wandering Wallygagglers of North Moor is all about this pod and their original search for a home," Draco says. "There's got to be something useful in there. If nothing else, a list of reasons why other places wouldn't do."

They keep reading.

There might be something to this bezoar-likeness idea. Granted, he knows nothing about breeding plants. Or what it's like to add them to an environment that's already functioning smoothly. It could be problematic.

"It says here they ended up in a moor once that was already occupied by Fenny snakes and had to leave," Harry notes. "I can't tell if they became prey or had to compete for the same resources."

"What do Wallygagglers eat?"

Harry thinks. "Question for Luna."

Draco pops a custard cream into his mouth.

"Potter," he says, "do you think—" the rest of his words come out as a series of chirps.

Harry looks at him, startled, and his eyes go wide. He lets out a laugh so open and unguarded that Draco almost doesn't care about what caused it.

"Holy shite, Malfoy. I had no idea, sorry." But he's still laughing, nearly sliding out of his chair.

"Fuck you," he says, though all Harry hears is a bit of sharp, angry tweeting, which sets him off again.

"I didn't know, I swear I didn't know," Harry chokes.

Draco isn't amused, but that has more to do with the fact that when he tries to lift his hands, his wings rise up instead than it does Harry's incessant laughter.

"You make a very fetching canary," Harry tells him.

Draco does not preen; he'd rather die than give Harry the satisfaction.

"Oh, Merlin, if Ron were here." Harry snorts. "I can't believe he missed this. Merlin, I wish I had a camera."

Draco lets out an indignant chirp.

"Oh, come on, Scorpius would get a kick out of this."

Draco rolls his eyes. That's certainly not enough reason to do it.

"First to fall over when the atmosphere is less than perfect," Harry sings. "Your sensibilities are shaken by the slightest defect—"

Draco squawks in confusion. Merlin, Harry's voice is grating. He was not made to be a singer. There are very few instances in which Draco would encourage him not to quit his day job, but this is one of them.

"You live your life like a canary in a coal mine!" Harry bellows, punctuating the line with a laugh. He tones his voice down. "You get so dizzy even walking in a straight line."

"I hope you're done," Draco says, and for the first time it comes out like real words, although slightly warbled. He coughs sharply, surprised to have regained usage of his voice, and then he rejoices. "Show's over. I'm not feathered anymore."

Harry grins back at him, loopy and far too fond, and Draco feels his heart stutter.

"You're a wretched singer, by the way," Draco says.

"Now," Harry replies, and though he's stopped singing, his voice drips with humour, "if I tell you that you suffer from delusions."

"And if I tell you to shut it."

Harry shrugs. "Well, we reach an impasse, don't we?"

"So it would seem." Draco considers the tray of biscuits again. He's still hungry, but he doesn't fancy being turned into any other large, fluffy, yellow bipeds. "What is that horrible song even about?"

"Well, you know ... coal mines. Canaries."

"Mm, but what's the relation?"

Harry meets his look blankly. "You ... Surely you've heard it. That can't be just a Muggle phrase."

Draco waves dismissively. "Of course it is. All the stranger ones are."

"A canary in a coal mine," Harry says again, like the problem might have been not emphasising which words were the important ones the last time.

"A Boggart in a broom cupboard," Draco returns, equally meaningless.

Harry sighs. "Really?"

Draco smiles patiently.

"All it means is, like, a warning sign. Not too long ago, workers would take canaries with them when they were going mining. Because canaries are smaller or more sensitive, or something, they—" Harry cuts himself off, eyes going wide.

He jumps to his feet and races to the door. "Parvati?" Harry bangs hard on the wood. "Rolf? For fuck's sake! LUNA? Someone who knows shite about magical — Kreacher!"

The elf appears with a pop. Draco, though he still isn't sure what's going on, curses himself a few times for not being as smart as Harry Potter. Of course the fucking house-elf could help them get out.

"Does Master want something?"

"Wallygagglers have a different magical composition than human beings, right?"

"Does this surprise Master? He does look remarkably similar to one of the beasts."

"They also must have different physiology."

"Is Kreacher needed here?" the elf asks.

"Yes! Kreacher, is it possible that ingesting magic could affect them differently than it does us? That they're more sensitive to it?"

"Why is Master acting as if this is a revelation? Is he truly as simpleminded as Kreacher has always thought?"

"A-ha!" Harry yells, picking up the elf and spinning him around in a delighted circle.

"Master will not be—"

"Unlock the door."

Kreacher does so with a begrudging snap, and Harry finally sets him down.

"Sorry! Got to run." He bounds across the room and grabs Draco's hand, jerking him along, all the way to the sitting room.

Granger is the first to see them, her mouth dropping open in a little 'o' of concern. Everyone else turns to them in surprise, and Teddy even looks quite indignant.

"Now, how did you—"

"The Wallygagglers aren't the only ones affected!" Harry exclaims. "That's why drinking the water directly still hurt me! It's not because the water is so much more concentrated. They're just more sensitive to it than the rest of us. They're the canaries."

"Er ... mate?" Weasley says. "Did Malfoy hit you with a Confundus Charm in there?"

Ridiculous. He doesn't even have his wand, and Draco is hopeless at wandless magic.

"The canaries! In the coal mine!"

Granger gasps, and her hand flies to her face as she's the first one to grasp his theory. "Oh, Harry, that's brilliant. I think you're right. I mean, it makes total sense."

"Explain it for the class, then," Lavender says.

Granger sighs impatiently. "Before the late eighties, coal miners in the Muggle world would bring canaries into the mines with them to sense when the air was getting too full of carbon monoxide."

"Er?"

"Basic science, Ron. I'll explain in a moment. The canaries would be affected before the miners because of how sensitive they are to adverse conditions, especially toxic gases, and having that early warning time would save the miners' lives. Actually — it's fascinating, canaries have air sacs throughout their bodies like most birds, rather than the diaphragms so common in land mammals. When they exhale, they're actually absorbing oxygen, whereas humans can't even properly expel their carbon dioxide all the way. It takes canaries two full breathing cycles to—"

"Mione," Harry whines.

"Sorry," she mouths, miming zipping her lips embarrassedly.

"I thought it was interesting," Weasley offers, and she beams at him.

"Anyway, they were affected before the miners. By the time humans felt ill, it would be too late." She looks up at Harry. "You don't think...?"

"I do."

"You do what?" Parvati asks, like she already knows the answer.

"We have to come up with a solution quickly, before wizards start dropping too," Harry says.

Everyone goes quiet.

"At least..." Scorpius hedges, "at least this gives us plenty of ways to convince the Ministry that displacing the Wallygagglers isn't the solution."

"If we're lucky," Lavender says. "If the prats will listen to a word we say."

"We could go straight to the papers," Luna suggests. "I could put an article in The Quibbler the moment we get out of here."

"They'd call us alarmist," Granger disagrees.

Rolf, who has been frantically flipping through a journal since the moment Harry announced his theory, finally looks up. "What do we reckon are the odds that they process other kinds of magic differently too?"

"What do you mean?" Draco asks.

"Potions, counter-curses, all the things we couldn't quite get to work for humans. If Wallygagglers are more sensitive to the spells originally, what's to say the solutions we've come up with so far wouldn't work for them?"

Harry lights up. "Hey, you're right!"

"But if eventually this is going to spread to wizards too..." Parvati says.

"We'll have to be ready," Rolf agrees. We'll keep working until we come up with something. Or until we can convince the Ministry to order Gringotts to find a better way to deal with the castoff."