Disclaimer: Taoism: Not mine. Zen: Can anything ever really belong to anyone? Firenze: Mars bright in the seventh house tells you a lawsuit is on the ascendancy if you claim they are yours. Yoda: Mine they are not. Elsa on Caffeine: zubzubzubzubnotminezubzubJKRandWarner'szubzubzub. Severus Snape: Write something original and stop tormenting me, you insane, chocolate-crazed Muggle bint.

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Chapter 23: Fun and Games in Potions

The dungeons hadn't changed much. In fact the only change Snape would make would be to make them slightly more cheerful. Harry wouldn't have believed it if he hadn't seen it with his own eyes. He wished he had a camera. They went down the stairs accompanied by Rosier and Avery; Harry kept a careful eye on Avery – he didn't trust the pudgy boy, and not only because he reminded him of Dudley. Despite himself he was finding it hard to dislike Rosier. He kept reminding himself that Rosier would one day be the enemy – and there was the possibility that he already was. Did he have the Dark Mark yet? But the uniform was just the same now as in the future, and there was no hope of seeing anyone's forearms. Harry was grateful yet again for the disguise Snape had put on him – he didn't need any trouble because he looked like that complete anti-Slytherin git James Potter.

He was doubly grateful to the strength of the charm when he felt something push into him from behind.

"Oops," said Avery. "My mistake."

"What the hell did you just do?" Harry snapped, aware that the edges of his face were tingling.

"Thought you might have been some Gryff sent in to spy on us," Avery said, smiling. He twirled his wand. "Well, there don't seem to be any charms disguising you."

The next second he was slammed back against the moist stones of the wall. Snape's arm was across his throat.

"Le… le… let me… go…" Avery gasped.

"You stupid piece of slime. Did you think that was funny?" Severus shoved harder. "Well? Did you?"

"Ack!"

"Snape!" "Severus!" Rosier and Harry hissed. They each grabbed a shoulder and pulled Severus off Avery.

"Leave him, Snape. Not here, anyway. Boggle'll be down here in a minute."

Snape growled but pulled back. He fished in a picket and pulled out a folded piece of paper. "Oh, bugger it," he snapped as he saw the new line of green writing down the bottom of Dumbledore's permission slip. "Avery, you complete and utter wanker. You've just lost us ten points for impeding research."

Rosier joined him in glaring at Avery, who wilted and scurried into the Potions classroom.

Rosier sighed. "Idiot," he muttered to the air in general, and stalked after Avery.

Severus checked the charm on Harry. "It's fine," he whispered.

Harry grinned. "It took Dumbledore two tries to break it. Nice."

Severus smirked back. "Excellent. Come on. Your new friends will be in soon. Then again, maybe we should wait out here and see if they want to impede our research again."

But Harry didn't want another confrontation with his father. "That guy who looks like me and his mates? No, thank you – I'm already creeped out after meeting some of your Housemates. Didn't think much of that LeStrange chap and his girlfriend. The blonde girl seemed nice, though. Who's this Lucius she was talking about? Seemed like a friend of yours."

Severus looked fleetingly worried. "Lucius Malfoy. And he's not really a friend of mine. I don't have friends – it's a knack, I guess. I don't know why he's suddenly taken an interest in me. He never noticed me much when he was at school here – he's four years older. But he likes to keep an eye on things at his old school. He offered to put me up during the holidays. I considered it at Christmas, but my parents let me stay here instead. Thank God."

"I thought you hated it here."

"I do. But it's better than home."

"Really."

"Mm. Home is really boring." He didn't meet Harry's eyes, and pushed past him into the classroom.

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There was the spare stool where it usually stood – at the back of the classroom next to the cupboard storing non-flammable ingredients. Harry dragged it over to the table where Severus was sitting. In this time the Slytherins were all sitting over on the left, just like in Harry's time. He wondered who the other desks were for. He didn't have long to wonder.

The laughter outside along with Snape's scowl gave the Marauders away before they even opened the door. They went silent and glared at Harry as they came in. "Hey, Squit. Snivellus." Sirius Black swept past them.

Rosier yawned, covering his mouth with a languid, long-fingered hand. "That's ten points from Gryffindor for rudeness," he said.

Sirius snorted. "Moony, set him straight."

"Unfortunately he's allowed to do that," Remus said, sighing. He didn't look at Harry or Severus. Harry heard him whisper tiredly, "Remember what Dumbledore said."

Sirius growled like a dog. Harry guessed three of the four were Animagi by now.

"Are you sure you want to be in this class?" Severus whispered. "I mean, do you even like Potions?"

"I don't know," Harry said, unable to help adding, "Our Potions master isn't very pleasant and he's got it in for me. Believe it or not, he hated my dad at school and now thinks he can take it out on me."

"What a git."

Harry bit his tongue for half a second. "He has his moments. I think if we had a better teacher it could be a really good subject."

Severus nodded. "I rather like Potions. After DADA it's my favourite subject. But I only really enjoy it when we're allowed to do independent research. We're doing bog-standard stuff today – about as interesting as watching grass grow. I could just about do it in my sleep."

Rosier, whom Harry was liking more after his defence of him and Severus, leaned back from where he was sitting just in front of them. "Don't let him fool you, Lovegood," he said. "Snape could do it in his sleep. Boggle will be in in a minute and I'd better warn you that he doesn't like Severus – even though Boggle's our titular Head of House. Snape's a threat to him because he knows Potions backwards and can explain it better than our so-called teacher with forty-odd years of experience."

"Stop being nice," Severus growled. "It's getting on my nerves."

"I'm not being nice to you, numbskull. I'm being nice to a guest from another school. Just to prove that some of us," he added, raising his voice fractionally so that Lupin, who was sitting across the aisle from him, could hear, "have the manners our parents raised us with."

Lupin ignored him. He was looking a little tense. Harry wondered how long it had been since the last full moon. James and Sirius (Peter wasn't in this class, it seemed) leaned back in their chairs. By their expressions they were about to say something and Harry was taking a morbid pleasure in wondering what it would be, when the door opened. It didn't slam back on its hinges like it would when Snape was Potions master, but it did get their attention.

An elderly man in faded green robes and with a mouth like a purse with the string drawn tight stamped down the aisle. He slammed his papers down on the lectern. If Harry had ever thought Snape had a miserable attitude towards teaching, he had a new standard with which to classify miserable attitudes against.

"Page sixty-three," the man barked. He sounded like a seal. He gave Harry one cold look-over with clouded eyes like those of a day-old dead fish and then pretended Harry wasn't there. "Get on with it."

Then he sat down with a large pile of essays, a quill and a bottle of red ink, and proceeded to ignore the students en masse.

Harry looked at Severus, who didn't seem to see anything amiss and was pulling out Potions ingredients from the student cupboard. "Want me to help?" Harry asked.

"Students are to work individually," droned the bent head of the Potions master, not bothering to look up.

Severus gave Harry a quick smile and a shrug. "I'm fine," he murmured. "Why not do some reading?"

"… In silence," Boggle growled.

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It was a boring lesson. Even by Potions standards. Harry amused himself dividing his time between taking notes from the book on myths and legends and watching Severus. The Slytherin seemed calmer when working over a cauldron, and sure of himself as he wasn't outside this room. He had his potion brewed and the correct colour while some of the other students were still dicing their beetle legs.

Or it was boring for the first two thirds. At that point, Sirius tried to fling a newt spleen in Severus' cauldron, but Severus flicked his wand and it bounced away.

Into Lupin's cauldron.

Which began to foam.

"Snape! You pillock! What did you do to my –?" Lupin spluttered as he peered dubiously into his cauldron.

"Lupin, you great thick idiot, get away from it!" Severus grabbed Remus by the back of his robes and yanked.

Remus went flying backwards and landed on the floor, leaning against Harry's legs, where Harry put a hand on his shoulder to steady him. Remus opened his mouth angrily, then paused.

His cauldron was beginning to rock on its little stubby legs. "What the…"

There was a noise like fwooom! and rainbow sludge shot up towards the ceiling.

"Everybody get out!" Severus shouted, grabbing his wand and flicking it in a complicated pattern at the ceiling. Long viscous strands which had been dribbling back down towards the students' heads froze and hung like multicoloured stalactites. "That won't hold it long," Severus said quietly. But he paused to bottle a sample of his potion and dump it on Professor Boggle's desk. "Professor – that stuff's highly toxic. Black put a newt spleen into an unfinished potion."

Boggle glared at Severus for half a second before his expression froze and he went white. He leaped up and shoved past Severus, knocking him back against a desk.

Moving like lightning, Professor Boggle flew out of the classroom. "Everybody get out!" he shouted at the stunned students, his voice dopplering as he bounced off the doorframe and raced away along the corridor.

There was a mad scramble which left Harry, Severus and Rosier alone in the classroom. The door banged shut.

"I say, Snape – is that stuff really as bad as Boggle thought?"

"Yes," said Severus mildly, rubbing at his shoulder which had been hit by the corner of a desk with one hand while calmly putting out the fires under the cauldrons with his wand in the other. "Harry – get the other fires, will you?"

Harry hurried to help, aware that Severus was keeping a very, very careful eye on the hanging rainbow stalactites. Rosier shifted from foot to foot, clearly wanting to bolt with the others, but he stayed and extinguished the rest of the fires with Harry and Severus.

"There really needs to be a charm that can put all of these out at once," Severus sighed. "Now… accio lids." Lids for the cauldrons shot out of a cupboard. Severus ducked just in time and they clattered against the desk behind him. "These cauldrons need to be capped. If any of that stuff gets into them the contents will also turn nasty. Nastier – because it'll turn into an aerosol. And I don't know how well the ventilation is maintained around here. You never know if it'll get into the school system."

"That would be bad?" Harry asked.

Rosier, pale faced, nodded. "That would be extremely bad. Snape, how long is that spell going to hold?"

Severus, putting the last lid on the last cauldron, squinted up at the ceiling. "It's wearing off now. And no, I can't reapply the spell. It destabilises the binding power of the aqueous medium – meaning that it's going to boil and vaporise if I try it again. Let's get out of here."

They scurried for the door. But there was a small problem.

"It's locked," Harry said, yanking at the handle. He took out his wand. "Alohomora."

It was still locked.

One of the rainbow strands above them began to grow, oozing down towards the floor. The trio leaned up against the door to get further away from it.

Severus was breathing harder. His normally pale skin was off-white with fear.

"We're trapped."

"A fireball should blast that door right off –"

Severus grabbed Rosier's wand hand. "No! These doors are fire resistant. Throw a fireball at them and it'll bounce back. Want to know why I put out all the fires?"

"Oh. Flammable due to combination of sneezewort and peatpallum. Right. So what do we do, then?"

"Bubblehead charm?" Harry suggested.

"Can you cast one big enough for all of us?" Severus asked. "If any of the fumes touch your skin you can absorb the toxin that way."

The stalactites were growing longer. Harry had a flash-back to Fluffy, dribbling long streams of drool as he prepared to attack.

Harry shut his eyes and tried to remember the spell Trudi had taught him. He whipped his wand around in a circle, compensating for the extra two people.

Pop.

The Potions classroom grew distorted. The bright stalactites dimmed a little, shading to green and purple and blue. It was like being inside a large, blue, upside-down fishbowl. A thick stream of the gloop slid down the side of the spell. It had landed right over Severus' head. Severus swallowed. "Good job," he croaked.

"Yes. Jolly well done," Rosier added shakily.

"Thanks," said Harry. "Now how long will it take before someone comes to let us out?"

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It didn't take more than a minute before the door creaked open and Remus Lupin poked his head through. He had a handkerchief over his mouth and his wand at the ready. Harry grabbed Severus and Rosier by the elbows and marched them towards the door. As they passed through, he let go of Rosier and poked the bubble with his wand. It popped. The three boys darted through the door before they could have anything drip on them, shoving Remus back into the corridor as they went. On the other side they yanked it shut. Severus leaned against the wall, breathing heavily. "Well, at least we managed to show you a typical Hogwarts class."

Harry grinned. "Yeah. And I thought it might be boring."

Rosier slapped him on the shoulder. "That was a bloody brilliant spell, what? One hundred points to whatever school you're from."

It wasn't very funny, but they'd all just survived something that could have killed them. Laughter came easily at that point.

"Are you three all right?" Lupin asked, a line of concern drawing his brows together. "What happened in there?"

"Well, newt spleen should never be added to a reducing solution. I don't know how or why Black had one, but it must have –"

"I beg your pardon, but I clearly remember you throwing that spleen into my cauldron," Remus said coldly. "Why you insist on shifting the blame is –"

"Sirius threw it into Severus' cauldron. Severus knocked it away." Harry shrugged. "Maybe you should check your vision."

"And if I'd known ahead of schedule that it was going to be a newt spleen he was throwing around like a quaffle I wouldn't have aimed it at your cauldron. Mouth, maybe," Severus sneered. "I suppose I should thank you for opening the door and letting us out, but as I'd just saved your life I don't think I'll bother."

Remus rubbed at his eyes tiredly, looking closer to the age Harry remembered him. "Severus…"

"Don't call me that. You're not my friend. And I expect it was one of your friends who locked the door, thus trying to kill me."

"Snape, then. Thank you for making sure I got out of the way. And I'm sorry someone locked the door – I don't know who. It wouldn't have been Sirius or James, though. They were out just after me. They've gone up to find Dumbledore to sort out the mess."

Rosier checked the door. "I thought for a bit it was deliberate, too, but look, chaps." He nudged Severus aside and opened the door (ignoring their protests). He slammed it back and the lock bounced up and clicked down. "See? This lock snaps shut when you close the door hard enough. I guess it's got a special locking hex on it to be resistant to the unlocking charm."

"It needs to be fixed," Severus said, folding his arms and glaring at the lock like he was practising for the future Neville Longbottom. And it would be fixed, Harry knew. Otherwise, given Snape's dramatic entrances, every Potions lesson he'd ever taken would have ended with someone needing to call for Filch to come and open the door for them.

"Is Professor Boggle still inside?"

They jumped. Harry turned to see Dumbledore, trailed by James and Sirius.

"He's probably still running," Severus said dryly.

"Oh, I'm sure things aren't that bad."

"Newt spleen in an arristo potion that had been brewed for no more than ten minutes, thus reacting with the unchelated hydrophilic pyrognostic compounds which had just been released from the sneezewort by dissolution in the presence of peatpallum in a weakly alkaline solution with a pH of between eight and eight point seven. It became unstable and erupted, plastering the ceiling. The result was a sticky, viscous liquid which refracts white light and separates it out into the visible spectrum and probably a little way into ultra-violet, but I didn't have time to check. I froze it with a modified petrification charm which unfortunately can't be used again. Other cauldrons with the potion at similar stages of brewing were open over low, naked flames. The corrupted arristo potion was at a point where it could splatter and start a chain reaction in the other cauldrons, reaching a critical mass where the aquatic hydrogen-oxygen dipole would begin to exhibit magically-influenced characteristics and loosen the hydrogen bond keeping the aqueous medium liquid. This would catalyse the decay of other hydrogen bonds in the other cauldrons, thus precipitating a mass aerosol formation and spreading the ptarmicoid thaumotoxin through the air. I don't know how good the dungeon filtration system is, but I doubt it would have been adequate for something this large-scale."

There was a stunned silence. Five out of the six listeners had been lost at 'unchelated'.

Dumbledore nodded, the only one whose eyes weren't spinning with the overload of information. "Very grave indeed. Thank you for your quick action." He waved his wand at the door, which sealed itself. "And for raising an interesting question of safety within the Potions classroom. Well. I shall endeavour to uncover Professor Boggle. No doubt he has gone to find Mr Filch."

"With all due regard, sir, I don't think this is something Mr Filch should have to deal with. It requires rather strenuous use of magic to clean up a mess like that. Plus you need a solid personal shielding charm to make sure your body doesn't make contact with any of the ptarmicoid in its thaumotoxic form. And lots of scrubbing."

Dumbledore smiled slightly. "As you would know, I seem to recall from your third year. But in any case Hogwarts wasn't using that tower… I doubt we have another room to take over as a Potions classroom, however. Well. Sirius. That was your newt spleen, wasn't it?"

Sirius shifted uneasily and ran a hand through his shaggy black hair. "Yes, sir. But I didn't mean to –"

"Of course not. And I'm sure you are keen to make amends for your unfortunate mistake. I shall ask Argus to supply you with all the buckets you need. Don't use any more charms on the volatile solution – as Mr Snape explained, he used a variation on a petrification charm, which means that the intermolecular bonds are in a rather fragile state and may be completely broken if subjected to another dose of a holding magic. If you need any further help understanding the dangers of what you will be facing I suggest you ask Mr Snape for advice. Oh, and Severus? One hundred points to Slytherin for averting a disaster."

"Th – thank you, sir." Severus looked a little dazed.

Given the look of murderous rage on Sirius' face and the way his fists were clenching, Harry thought it might be wiser to stick close to Dumbledore until they were among a crowd of witnesses again. "Come on," he said, grabbing a still stunned Severus and dragging him along the corridor.

Rosier winked at Remus and strolled after them. At the top of the stairs out of the dungeon Rosier nodded in that friendly way of his, although Harry didn't like the expression of evaluation that made his handsome features more fox-like. "Nice work, Snape," he said. "You know, talent like that could get you far."

"Yeah," Severus muttered as he and Harry headed towards the library. "Far from here, with any luck."

Harry looked back to see Rosier disappear in the direction of the main doors. Rosier was likeable in his way, but Harry couldn't reconcile himself to Rosier's future. Death Eaters were not meant to be likeable. Best if he remembered that.

He followed Severus, who wasn't one of Nature's likeable people but should still never have been a Death Eater. He stopped in the door of the library. "Oh. Damn."

"What?"

"That book on myths. I left it in the Potions classroom."

Severus winced. "It'll be a ruin by now. Oh well. Wasn't your fault." He sighed. "Shall we tell Madam Pince now or later?"

"How about after I've gone?"

"How about I go with you?"

Harry grinned, then realised Severus was serious. "I…"

Severus shrugged. "Think about it. I know – there's the whole 'universal conservation of mass' issue – but there must be some way around that."

"I'll think about it," Harry said. Imaginary Hermione was silent on this one. She must have known that some lies were too big and too obvious for Harry to need her to explain them to him.

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