Disclaimer: Didn't write the Harry Potter books… big shock I know…

Oblivious that he was the topic of conversation for his House Masters, Marmaduke was trying to explain to the other Slytherins just what he had done to the door.  In the background, over his shoulder, he could hear people arguing over what had caused them to turn invisible.  The heat was obviously getting to people, some of the girls were fairly screeching at each other.  He himself was beginning to sweat profusely.  A knot began to tighten in his stomach. 

"Everyone shut up for a minute!"

To his surprise everyone did, startled by the ferocity of his voice.

"Okay, now please don't kill me or start to panic," as he uttered the last words he could feel the air in the room change from mild irritation to that of unease, "I think we might be in more trouble than you all realise."

At this Pansy interrupted him, "Believe me DeVries we are well aware of the trouble we're going to be in once we get out of here.  I'm going to have to explain to Snape just why I missed his lesson as is everyone else stuck here.  I can't believe you were so stupid!"

As Pansy drew breath to continue her rant Marmaduke quickly continued his speech, "Yes, well, that'll be a problem later.  But what I meant is that right now, I think we're running out of air."  The statement was met with deathly silence.  He supposed that was a good thing, at least no-one was wasting the remaining air in the room.  The next minute he found his feet swinging madly above the ground as he was lifted up from behind.

"What, precisely, do you mean by that?"

Stuttering somewhat, as he struggled against his tormentor, Marmaduke hastily explained, "You see, this wasn't a simple locking spell.  It's one that was used to defend castles against attack.  It completely seals the area.  It's an unbreakable barrier, nothing gets in or out."

"And this includes AIR???" several voices chimed with disbelief.

Marmaduke nodded sadly, then realized that he couldn't be seen, "Yes, I think so."  He was dropped unceremoniously to the ground.

"Let me guess," a sarcastic voice called out, "this spell you used, isn't related to the any of the common or garden variety of defensive spells that we might come across in our textbooks."  The voice didn't even give him a chance to answer, "Brilliant, bloody brilliant.  Trying to find a counter 'll be like looking for a needle in a haystack."

Deciding that there was a danger that the situation could get out of control Pansy moved to impose her authority, "Shut up everyone!  We need to conserve the air, so no talking unless strictly necessary, which means no talking.  We need to reverse the spell so we're going to take it in turns to have a go.  Those of you who think they might have an idea on what to do; line up to the left of the door.  Place your hand out in front of you so that you know you're not at the front.  Once you get to the front try out whatever you think might work.  Everyone pay attention and try and use other people's ideas to build on.  Right, get to it.  We'll worry about the invisibility once we get the barrier down."

There was very little mumbling as people lined up, the gravity of their predicament had sunk in and in a manner that would have surprised the children of the other Houses, the Slytherins set themselves determinedly to their task.

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Two floors beneath them two of their housemates were sat on the floor poring over the contents of the fifth Book of Death. 

"Here it is, I remember one of my cousins telling us about this augmentation spell that caused someone's head to explode!"  Blaise's childish enthusiasm would have been sweet were it not for the rather grotesque subject matter.  Next to him Draco shot him a look of distaste, rolling his eyes as he remembered that he couldn't be seen.

"Whilst I applaud your family's love for all things gory, how does this help us?"

"Oh, don't be sick!  I wasn't suggesting exploding someone's head you eejit.  That was just a freak result from a miscast of the spell.  See, what's s'pposed to happen is that the caster's thoughts are augmented and can be focused into someone else's mind."

That was, Draco thought, rather cool.  He was impressed with Blaise for remembering where to find the spell and thinking of its use now.  Of course he wasn't about to let Blaise know this so he merely said, "Right then, let's give it a go."

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Rosie

Rose Parkinson, Pansy's little sister, sat bolt upright upsetting the person next to her.

"Did you hear that?" she asked of no-one in particular.

"What?"

Rose, it's me.

"That!"  Rose was starting to feel a bit alarmed.  "That voice saying my name.  You heard it right?"

They can't hear me Rose, I'm in your head.

Rose by now was more than a little flustered, twisting and turning her head around to try and locate the voice.  Unaware of her reaction, Draco continued to speak to her.

I need you to tell everyone that when they get out they need to say that I was in the common room with you guys.

"Can't hear anything, you must've imagined it"

Panic did not come close to describe the emotions running through Rose's slight frame.  She began to hyperventilate attracting the attention of her sister.

"What's up?"

Did you get that Rosie?  You need to get everyone to get their stories straight.  Everyone has to say that me and Zabini were with you guys the whole time.  OK?  Dammit Zabini, there's no way of knowing that she's getting this.

"Draco?  There's a voice in my head, I think it's Draco." 

Pansy carefully regarded the space where she deduced her sister was sitting.  Her baby sister was a pain more often than not, but she didn't usually tell lies to get attention, nor was she likely to crack in stressful situations.

"Alright, I'll play along, what did he say?"

"Well, he said that everyone has to say that he and Blaise have been in here the whole time.  That's it really, he didn't say why or anything."

Pansy considered for a moment.  Her sister didn't sound crazy, and it made sense that Draco and Blaise might have done something that would require an alibi, especially if they were invisible. She raised her voice and addressed the room,

"OK everyone, listen up.  When we get out of here if anyone asks you're to say that Malfoy and Zabini were with us the whole time.  This is not up for discussion and remember we're running low on air so don't waste it gossiping!"

Pansy wiped the back of her hand across her brow.  It was getting progressively hotter.  She was sure that that was not a good sign.  Some of the others had conjured little fans to keep cool, but though they gave comfort from the heat all they did was push the air around the room.  Not being an expert or having much experience in such situations she knew that they were probably safe for the time-being, but with over thirty people and no fresh air supply the situation was definitely not good.

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A/N:  See, told you this would go up fast.  Seems like following a bout of writer's block you get blessed with an insane period of energy. 

As ever let me know what you think, and that you are still reading.