Hermione showers in Myrtle's washroom.  She knows she's needed that since she had all that sex.  She hopes nobody was offended.  Myrtle isn't offended.  The ghost can't take her eyes off Hermione.  Moaning is involved.
Hermione gets up the next morning at the same early hour for the same reason.  She needs another book from the library.  She's been thinking about how she'll treat those Slytherin students.  Most of that thinking was about the way they've tormented her friends and herself.
She runs into Cho on the way again.
"G ... Get any last night?" the shy Ravenclaw asks boldly.  "Y ... You didn't talk about any, but y ... your body was blatantly post-c ... coital when we saw you in that invisible skin."
"It wasn't my idea.  Don't bring it up around Ron, please.  He might not understand," Hermione answers.
"D ... Did someone ..." Cho starts to ask.
"Remember I said I distracted all those Slytherin in the dark circle?  You don't want to know how I distracted them, not the details anyway," Hermione gives an answer that quiets Cho.
They get right past the librarian since they're going to shelves that aren't dangerous.  Cho offers the book on multiple orgasms to Hermione.  She turns it down and starts looking at volumes on group sex.  Cho relates that to Hermione's distraction.  Hermione's interest in a book on bondage and discipline doesn't relate.
On their way to breakfast, Cho asks, "H ...How much did you get with all that d ... distracting?  Did you l ... like it?"
"I couldn't count how many times they did me, but there were at least seven boys who got turns ... and one girl," Hermione makes Cho gasp.  "The physical sex was terrific.  Wore me out.  There wasn't any love, though.  Those guys didn't care anything about me."
Those b ... books look dark.  This isn't l ... leading you down a p ... path, is it?" Cho is getting concerned about her oversexed friend.
Hermione defends herself and reveals some of her plan, "This book on group sex is to learn about, not do again.  This other one is for ideas.  Just what can I do to them as their powerful, dark mistress?"
Cho's mind runs wild with that thought.  She gets a sly smile that grows larger the more she thinks about it.
"W ... Whatever you do, make sure they get caught at it.  The more embarrassing, the better," Cho suggests.
"Oh, yes," Hermione agrees.
They have the usual warm greetings from Harry and Ron that go beyond friendly.  Most of their classes go as usual.  It's between the classes and around the meals where they overhear Slytherins discussing their experience.
"It truly did summon the Dark Lord, didn't it?" Draco Malfoy claims his success.
"And then he burned up to nothing," answers another.
"That was because of the new mistress.  My summoning series still worked.  Admit it!" Malfoy gets belligerent and the other really has to agree.
She hears another pair of boys, one who was apparently there and one who was not.
"... and she took us on - all the boys, Nigel twice and even Wilhelmina," said the one.
"Wilhelmina?  A girl?" the second wonders.
"A girl who likes girls.  Now pay attention," the first goes on.  "She said all that wasn't enough.  She commands us to service her.  Just think - shagging a powerful witch."
"You mean serve her?" the second is still incredulous.
"ServICE is what she said, and she meant sex the way she said last night wasn't enough," the first explained.
At another time, Hermione hears Wilhelmina, the girl who wanted tongue, "That witch is so dark - she seduced us all and even made the Dark Lord burn.  If he was worthy of devotion, this new one must be."
"The Dark Lord shared his power with all his followers - made the group strong.  How will we get any strength to dominate the school from this new one?" asks Pansy Parkinson in return.
Hermione searches her memory.  She didn't see or hear Pansy anywhere around that fire.
"You had to be there to feel the power, to feel your wand being wrenched from your hand, to have your ass kicked all the way out of the clearing," answered the first.
"That still doesn't say how we'll get any of that," Pansy complains.
Hermione drags Ron away from supper a little earlier than any of the other Gryffindor.
As soon as they get into the commons, she asks, "I missed it with you last night.  Would you like to get together in your room again tonight after studies?"
Ron answers by his actions.  He reaches around Hermione and lifts her with one hand under her seat.  His other hand holds her chest tight to his.  His kiss starts gently and builds passion as long as he holds her.  He suddenly drops her and leaves her gasping after she felt the heat in that kiss.  She looks around to find Harry staring at them with other Gryffindor climbing through the picture frame.
"That answered the question," she tells Ron.
"But why wait 'til after studying?" from Ron brings a scowl from Hermione.
The only studying Hermione does is in the book about group sex.  She looks up gang rape and realizes she had it easy.  They were after sex, not out to hurt her - at least up to the point where she got away.  She wonders how they would have acted if they'd known it was Hermione they were screwing.  The book tells of some not-very-sexy ways gang rape can go.
The book also tells of group dynamics and pressure like that put on the virgin boys.  She starts thinking of ways to use that.  Maybe the other book has something about that.  It does get into the use of magic a little.  Hermione scares herself with that thought.  That would be truly dark, but it seemed like a good idea to her for a moment.
Ginny is out of the room, so Hermione slips into her catsuit of invisibility right there.  She stashes her nightshirt behind the tissues in the washroom again.  That really disappoints Myrtle, who only got a glance of Hermione's smooth gray skin.
On her way through, Hermione sees Harry with Ginny, Neville and several others in the commons.  He's telling stories - something about the Dark Lord and a fire.  The chances are better than she hoped for some alone-time with Ron.  Maybe Harry really understands that kiss he saw.
She slips into Ron's room and pulls the hood off her head.  That doesn't startle him.  He was watching for something like that since he saw the door open and close by itself.  He hops off his bed, tosses his book down to the floor and seizes Hermione.  She gets his tongue in her mouth before she can even say hello.  He gets handfuls of her soft, smooth skin as he rubs and strokes all over her invisible parts.  She just goes with it.  He's doing stuff she enjoys.  The way she feels about Ron right now, she'd enjoy anything he did.
Hermione peels off the suit very quickly.  It hasn't been on very long.  He won't have to wait for any long, struggling peel.  She stands, presses her naked self against him and wraps her arms around his neck.  She doesn't have to wait for him to get aroused.  She feels his penis grow hard and erect in his pants.  Ron picks her up and lays her out on the bed.  She smiles up at him with eager anticipation.  Her arms and her legs are wide open to him.
Ron loses two buttons from his shirt in his haste to get undressed.  His dreams are about to come true again and he's in a hurry.  He's not in too big a hurry to treat Hermione properly, though.  He kisses around her face while his hands run around her chest.  Of course, her breasts excite him as much as they do her.  So do the kisses.  He kisses her ears and neck while his fingers work her nipples hard and erect.  The tingles on the mounds of her breasts turn almost to pain when he tweaks and twists her excited nipples.  Hermione gasps and sighs which lets him know how much she's enjoying all that.
He works his kisses down over her shoulders and upper chest.  He likes her firm strength under the smooth, soft skin.  He also likes the sight of her breasts.  That doesn't keep his mouth from them for long, though.  He's soon licking and nibbling at her erect nipples and getting the gasps from her again.  His hands roam lower over her belly, mound and legs.  She wriggles her hips when his light strokes on her inner thighs send more tingles through her.  She presses her mound and vulva against his hand demanding more attention at her most sensitive places.
All the strokes and touching near it start the wetness running in her vagina.  She presses against Ron's hand and tries to thrust her hips so that hand finds her vulva.  Ron keeps the pressure light and the teasing heavy.  Her squealing whine adds to the wriggling.  Her body wants him as much as her mind does.  He keeps touching around her vulva and the light, brushing touch is driving Hermione wild.
He switches his mouth from one breast to the other at the same time his finger strokes between her outer labia and lightly touches her inner lips.  When that first stroke gets to her clitoris, Hermione breaks into bucking orgasm with choked screams coming from her throat.  As soon as he knows that Hermione has gone over the edge, Ron slips his finger into her vagina.  Hermione is completely carried away with all the tingling sensations exploding from her vulva.  Ron keeps her going for a long time by alternately stroking into her vagina then out over her clitoris.  He has every reason to be proud that he put her through such a complete, intense orgasm.
Hermione comes down from that peak after a while.  She lies there gasping and recovering.  She soon feels ready for another round.  She pulls Ron fully up on top of her.  She gets excited immediately when she feels his weight and the pressure of his penis against her vulva.
This is when Ron gets to reap the reward for his attention to her.  She wraps her arms around his shoulders, holds his head in her hands and pulls him close for a kiss.  She wraps her legs around his hips, tugs a little to the side and pulls him into her.  She gives a little whine as he slides upward on her and their lips don't meet anymore.  She doesn't miss the kisses when she feels his penis inside her and the tingles it sends through her vagina.
Ron strokes slowly and gently at first to get everything sliding smoothly.  He doesn't want to hurt his lover.  He also knows she liked the way he did her the other night.  He keeps it slow to make it last as he adds pressure on her clitoris at the end of every thrust.  Each stroke in or out of her vagina and each little pinch of her clit bring a squeal from her.
Hermione understands the slowness.  She knows that Ron is trying to give her a wonderfully enjoyable time.  She can just feel the love in the way he got her started, the way he holds her now and all the passion he sends through her on every stroke.  She didn't feel any love in the sex last night.  There's sure plenty of love here tonight.  Ron really cares.
Her body feels the explosion of her orgasm spreading all over.  She loses all other sensations to that orgasm.  It doesn't have one distinct climax.  It keeps going and going as long as Ron's thrusts keep going.  The thrusts end when Ron's body goes rigidly tense at the deepest point of penetration.  He holds himself there all through his climax, then wiggles only a little more.
The screams and grunts end with them looking into each others' eyes.  Hermione raises her head and kisses him none too gently on the lips.  They both sigh and relax slowly, both well satisfied.
Ron rolls off and Hermione rolls onto him.  She lays her head on his shoulder and her body along one side of his trunk.  She's straddling one of his legs.  The wetness from her vulva drips and runs over his thigh.  If he senses that, he doesn't show any reaction.  Her hand lands on his penis.  It's soft now and it's dripping, too.  She doesn't mind.  Whatever is wet on it either came from her or was ejaculated into her just a moment ago.
They cuddle together like that with Ron running one hand up and down her back.  His other hand strokes her side with occasional trips to the side of her breast.  They talk about how the sex feels and how they feel for each other.  They don't exactly say the word "love" but they're getting close to figuring that out.
It takes minutes, but they become interested in each other physically again. Her hand is on his penis and his hand strokes her breast regularly now.  Things rise and attention to those things brings more arousal.  Erection is involved.
Hermione quickly hops on Ron, leaning forward with her breasts just brushing his chest.  She starts wiggling her vulva against the head of his penis.  She works it into herself before he can help.  His arms are around her.  His hands stroke over her back, around her shoulders and cup those breasts hanging down over his chest.  Most exciting is that his penis has been taken into her vagina.  Her warm wet body is pulling at it every time she writhes and wriggles her hips around on top of him.
She keeps that wriggling going.  She keeps her breasts brushing him, whether they're on his hands or his chest.  She likes all that as much as he does.  Ron reaches his caresses down her body as far as he can.  It tingles Hermione when he gets to her hips.  He hears her gasp and keeps up with what she seems to like.  She's sure doing what he likes.
Hermione reaches climax before Ron does.  She shudders and squeals her way through her orgasm, then lies still on top of him.  Ron starts doing the work.  He thrusts his hips up and lifts her as his penis slides in.  Hermione just moans with each movement.  This is totally dreamy.  She's lying against her warm, cuddly lover while he's pleasing her.
It's not quite that pleasing to him.  Ron lifts Hermione, rolls her onto her back and mounts her again.  His strokes and thrusts are faster now and he squeezes her breasts a little harder.  This pleases Hermione all the more.  She's being taken again.  He's acting like her ideal of a man and that thrills her.  She's not doing anything but letting it happen.  It happens - another orgasm, that is.  She and Ron reach climax at very nearly the same time.  They both get tense all over and strain as the sensations course through their bodies.  Ron collapses on her and they both lie there breathing hard and sweating.
That's how Harry catches them.  He can see all of Ron's bare back when he comes in the door, but Hermione is hidden under him.  Her head is under Ron's receiving her share of the kisses.  Harry can't see her and thinks Ron is doing naughty things to his pillow.
"Weasley!" Harry says.
Ron finishes that kiss before he looks around.  Hermione turns her head and looks at Harry from under him.
"Hello, Harry," says Hermione in a bright, bubbly tone.
We know her by now, don't we?  The sex has her perky and peppy again.
Ron rolls off and Hermione climbs out of the bed.  Ron pulls the covers over himself.  Hermione sits at the edge of his bed and slips into her suit.  Harry just watches each part of her turn gray and disappear.
"Sorry, Harry," Hermione sort-of apologizes.  "I'm not supposed to do this when Cho isn't here, but you caught us out."
She pulls the hood over her face and Harry watches her disembodied head turn gray, then vanish.  Hermione bends down, kisses Ron and runs her hands over his body under the covers.
He gasps while she says, "That was wonderful.  Absolutely wonderful."
The bright, peppy Hermione is also feeling a little mischief.  On her way out of the room, she gives Harry a little peck on the cheek of his face and a light pat on the cheek of his posterior.  Harry gives an "Eep!"
Hermione goes straight to Myrtle's washroom and showers in her suit.  She really needs the shower after that much sex.  She keeps the suit on because she wants to go skulking about.  She does skulk, but she finds nothing, except ...
Cho skulks from shadow to shadow toward the sports department.  She ducks into the Quidditch team dressing room.  Yes, she and Harry both have aspirations of places on the Hogwards team.
Harry comes along a few minutes later.  He takes that parchment from under his arm, holds it in front of himself and says something about being up to no good.  Hermione gets close enough to see this time.  She sees "Marauder's Map" on the outside of the parchment.  When Harry opens it she sees marks shaped like feet at places on a diagram that looks like the school.  Each set of feet has a name in a banner.  She sees "Cho Chang"  by the dressing room.  She sees a trail of footsteps and the banner "Severus Snape" moving along a hall.  She sees "Harry Potter" in another hall with "Hermione Granger" right beside it.
"Hello, Hermione," says Harry.  "Enjoying an evening of skulking after your tryst?"
Harry reaches in Hermione's direction and gets more than he bargained for when she teases him.  She bends her knees a little when his hand gets near.  He gets a handful of her breast.  He gasps and jerks his hand back quickly.
"Save all that for Cho.  She loves it, you know,"  Hermione tells him, then walks away.
Harry watches her footsteps and banner go toward Gryffindor tower.  He's confident he'll be alone with Cho this time.
The next morning, Hermione realizes that she has the library books she needs for the moment.  Somehow a lying in just feels right.  The alarm clock and Ginny wake her in time for breakfast.  Ron greets her with a big smile and a tight squeeze.  Harry gives some of the same to Cho.  The girls smile back just as big.  It's getting old for them, but all the students around feel obligated.  They just have to tease these four about the displays of affection.
Friday goes much like the day before.  Classes are about like normal, if Hogwarts classes are ever normal.  Cho and Hermione snicker every time they overhear Slytherin students talking about the mysterious, sexy dark witch.
Hermione's studies after supper are in the book on domination.  She's appalled that people would treat each other that way.  She's even more appalled that some would like it enough to become aroused.  She does find one thing she thinks she can use.  It's a ceremony as close to witchcraft as that book gets.  It involves a group performing a chant.  The words are meaningless.  The sounds convey sexual tension and excitement.  The book says that any further suggestion, such as the sight of a naked body, can drive the group into a frenzy.
This is delicious.  It's just what she's looking for.  She'll have to think a little about how to use it to her best advantage - that means to the worst disadvantage to those dark students.  She has time to think.  She has another date with Ron before the official bed time.
Hermione stashes her nightshirt and slips into her suit in Myrtle's washroom again.  She doesn't play with herself at all.  Who needs that when Ron's waiting?  Myrtle moans her disappointment.
Hermione skulks through the commons and boys' halls to Ron's room.  Harry is reading by the fire in the commons.  Isn't he nice?
Hermione pulls the hood off her head in front of Ron.  He gives the same reaction as last night - to seize her up into a passionate kiss.  There is one difference.  He's already naked.  She feels his bare penis rise and press up between her legs.  He lays Hermione on his bed and himself right on her.
He's at his most manly while his kisses, caresses and strokes cover her.  Hermione is thrilled again.  She just lies there letting it happen.  She can't help returning the kisses or wriggling her hips under him.  His hands bring her to orgasm again.  Her reaction is to arch her back with all her might.  That throws Ron off her and almost off the bed.
"Sorry," she squeaks as she pulls him to get him on her again.
Ron doesn't let her say any more.  He inserts himself into her at both ends.  His tongue silences her mouth with another passionate kiss.  His penis in her vagina brings muffled moans and squeals around that tongue.  The lovers go through their orgasm, more than one for Hermione, as well as they ever have.
They collapse and take their time relaxing.  Hermione holds Ron in place on top of her every time he tries to roll off.  She keeps reliving the passionate sex his weight reminds her of.  He feels sweaty and not that comfortable, even though he's lying on his softly firm lover.  He rolls off at last and starts to cool down.
Hermione is merciless.  She knows Ron can't see her body.  She wants him stimulated to another round as soon as he can be.  She grabs his wrist and puts his hand to her breast.  She starts in on his other parts, too.  She runs her invisible hand over his belly and legs.  She's soon cupping his testicles and tugging at his penis.
Ron's penis rises in her hand, but that hand is invisible.  He can see his erection and the effect on his skin every time Hermione pulls at it.  The sexy witch decides he's ready.  She pounces again.  She straddles him and begins wriggling against his penis.  She works it into herself with just a few wriggles and a little pressure.  Ron watches it disappear as it enters her.
Ron's hands roam all over the space between his crotch and Hermione's disembodied head.  He feels the girl he expects there.  Her breasts have the engorged feeling and erect nipples he's come to know.  Her belly ripples each time she wriggles to settle on his penis.  Her powerful legs flex each time she rises to slide him out of her.
As before, Hermione reaches one orgasm while she's perched on Ron.  She's exhausted and even satisfied.  She's too fucked out to do any more and Ron hasn't reached climax yet.  He rolls her onto her back again, mounts her and continues with the thrusting.  He knows by now just how hard to slam into her and just how to handle her breasts.  Hermione may feel satisfied, but she gets the stimulation he wants her to get.  They both reach another orgasm before they collapse.
Some heavy breathing, serious cuddling and a little dozing later, Hermione remembers that she has serious skulking to do tonight.
"Come on, Ron.  Show me the shower on this floor," she invites.
Ron's eyes go wide.  A girl in the boys' shower?  With him?
Hermione sits up and pulls the hood over her head.  She completely disappears.  She stands and tugs on Ron's arm.  He caves.  She won't be seen, will she?  He puts on his bathrobe and slippers.
They pass a few boys in the hall, mostly in underwear.  Hermione has had quite enough of what Ron keeps in his underwear tonight.  She's not thrilled but she is as curious as she was a few days ago.  There are several other boys in the washroom and two in the shower when they arrive.  Ron hesitates a little until he feels a push from the invisible Hermione.  He shrugs out of the robe and steps out of the slippers.
He doesn't feel anything from Hermione, because the young witch isn't right there.  She's skulking about the shower, checking out the other boys.  That's her curiosity again.  The thought just struck her that if she does what she plans, she'll be faced with the private dangly bits of a lot of boys.  She'd better be used to that.  She looks over those two boys quite carefully.  She also checks out Ron.  It's her lover who comes out ahead in the comparison.
Ron starts water spraying from one of the showers.  Hermione knows she'll appear as a void in the spray, so she stays at its edge and mostly hidden by Ron.  They're both thoroughly wet by the time those other boys leave.  As soon as they're gone, Ron and Hermione fight over the soap.  They both want to rub it all over the other.  Ron wins by tickling Hermione just below her ribs.  She barely stifles a shriek.
She has to stifle the moans, too, when Ron washes all of her with that soap.  He washes her face and neck, breasts, shoulders and upper back, breasts, all around her waist, breasts, hips and vulva and breasts.  He actually washes both of her legs before returning to her breasts one last time.  Hermione sighs the first few times he washes her breasts.  The later times, she thrusts her chest out proudly.  He thinks her body is sexy.
She likes his body, too.  She doesn't revisit any one part, but she enjoys giving all of him a lot of slow caressing.
They dry each other as long as they're the only ones in the washroom.  She gets most of Ron dry.  He gets her chest dry.  When another boy comes in, Hermione ducks around a corner to finish.  It's really easy to dry her head with no wet hair up there.
She leaves Ron with a kiss to his lips, a hand stroke along his penis and. "Tomorrow."
She skulks to the entrance hall and gets there a little after bed time.  Quite a few ambitious Slytherin come out of their dungeon.  They're talking about Voldemort, the Dark Lord, and this new Dark Mistress who's name they don't know yet.  It seems that first hand stories of the Dark Mistress are easier to believe than old tales of one who's now dead anyway.
The group of boys is now up to 13 - as many as the whole circle of the other night.  They're after power, yes, but they're mostly attracted by the promise of sex.  She did say "service" didn't she?
There are ten girls, including Wilhelmina and Pansy.  Only one seems to be looking for sex.  The rest are mostly looking for power or maybe lessons in this domination thing.
The whole group open the large front doors and start to step out.  They're face to face with Professors Dumbledore, McGonagall and Snape.
"Out for some adventure, are you?  The rest of your Friday evening shall be spent in boring detention. Professor Snape, I believe you have a suitable place," says Professor Dumbledore in an ominous tone.
Professor Snape ushers them to his Potions classroom.  They are to sit in there quietly and do nothing.  He will be preparing lessons in his office next door and will be listening.
Hermione has skulked into that room already.  She climbs to the top of a tall bookcase and sits near the ceiling above all the students.  She doesn't let the boredom get too punishing.
"Inaudius!" she intones quietly as she waves her wand around the walls of the room.
Her voice is low after all her moaning during sex with Ron.  She adds the tension in her throat and breathy quality.  The students hear her incantation for the charm and most look up where the sound comes from.  The ones who remember that voice fear her anger.  They're missing their wands and don't want to be missing anything else.  They see the Dark Mistress' wand floating in the air above them.
"You were to meet at the fire by the lake.  No matter.  You can do my bidding and service me here as well as there," Hermione says as strongly as her disguised voice can say it.
Draco Malfoy stands at the center of the room and challenges, "What's in it for us?  What can you offer?"
"Your survival!" Hermione's Dark Mistress voice exclaims.  "Somnola!"
She waves her wand at Malfoy.  That puts him to sleep and he falls straight down to the floor.  That in turn scares the crap out of everyone else in the room.  They stare up at the wand waving over them and see it disappear.  That's when Hermione put it back in her pocket.  Students around the floor stare up in awe with open mouths.
"Prepare to service me, all of you.  Move the desks to the walls.  Make room for circles," they hear from the Dark Mistress.
Desks are cleared and the students stand around waiting for what's next.
"Now strip naked, all of you," the Dark Mistress' voice is coldly quiet.
Most of them expected something like this, so they start removing clothes fairly quickly.  They're soon down to underwear.  Boxers or briefs still hide the boys.  The girls all have their panties and some are wearing bras.
"Naked!  Now!" the Dark Mistress' voice is a little more tense.
Some of the boys turn their backs and drop their shorts, but only some.  Hermione decides to make an example of the one who's been tormenting her the most - Pansy Parkinson.  Pansy is wearing only the skimpiest bikini panties.  The tight, tiny breasts on her skinny frame don't really need a bra.
Hermione climbs down from the bookcase and sneaks up behind Pansy.  She grabs the band of Pansy's panties at both sides and snatches them down to her ankles in one motion.  Hermione then pulls the panties hard toward her.  That pulls Pansy's feet out from under her and topples her forward.  It hurts a little where Pansy hits the hard floor.  Her head hits Malfoy's reclining body, though, and isn't hurt at all.  Her head goes right into his crotch and Pansy's chin is sharp.  Malfoy moans in pain.
Pansy says, "Eww."
"While you're down there, strip him," the Dark Mistress commands Pansy.
Pansy gets to her hands and knees and says, "Eeewww."
She gets the foot of the Dark Mistress on her bare buttock.  The kick propels her face into Malfoy's crotch again.  He gives another moan.  Pansy gets busy with the buckle of his belt.
Every stitch of clothes on the awake students hits the floor in the next ten seconds.  None of them really want their face in Malfoy's crotch.  Hermione pushes the now naked Wilhelmina toward Malfoy.
"Help strip him ... and leave her alone," the Dark Mistress knows what Wilhelmina will like the least.
The whole group is naked, but only a few are looking at each other - mostly the bold boys at the girls.  The girls try to turn their backs, but they're surrounded.  They have to leave something showing no matter which way they face or what they cover with their hands.
"Form two circles.  Leave sleeping beauty at the center," the Dark Mistress commands from high on the teacher's desk.  "Boys around the outer circle, facing in.  Girls around the inner circle facing out."
There are two more awake boys than girls, so they naturally make a larger circle around the girls.  Now they're facing each other and close.  There are more of the hands covering more of the places.
"Hands up in front of your shoulders, palms out," the Dark Mistress ends the covering.  "Gaze upon each other.  You do expect sex, don't you?"
The voice of the Dark Mistress teaches all of them the chant of meaningless words.  She moves on when she starts to feel the effects of the sound of the chant.  Yep, it's sexy.
"Move your circles in opposite directions.  Look at each one you pass.  Move!" the Dark Mistress commands.
The circles rotate and revolve.  Eyes flash from one naked body to the next.
"Now touch each body you pass.  You must accept ANY touch in return," the Dark Mistress moves to the next step.  "and recite that chant as you move.  You are to concentrate on keeping the circles moving and close to each other, touching each and every one in the other circle as you pass and repeating the chant, one beat to each step.  Let nothing distract you until I tell you to stop.  NOTHING!"
The circles rotate and the naked students tentatively touch each others' faces or shoulders.  Some of the more adventurous boys soon take the hint from the word "any" and the sense of the chant.  Their touches move to the girls breasts.  That's not enough to move the nervous boys to erections in that large group.
Slytherin girls are not to be outdone.  Their touches move lower on the boys.  They grasp at pecs and bellies.  They have to step closer to do that.  The circles soon get close enough that they can all reach down to touch each others' crotches.  The boys feel the gentle groping on their genitals and return the favor to the very close girls.  There's soon a rising penis at the front of each boy and many of the girls have wet, runny drops on their legs.
Draco Malfoy wakes up in the middle of the floor with those circles orbiting around him.  He's dazed, though.  It doesn't register.  He struggles and staggers to stand.  He wobbles and staggers toward the naked backs of the girls nearest him.
Hermione decides that it's time they got caught.  The first step is with Professor Snape.
"Audibilis!" She incants and her wand removes the sound suppression from the walls.
Professor Snape comes dashing into the room to investigate all that chanting.  He opens the door to find the back of a naked boy right in front of him.  Next is the front of the bony skinny figure of the completely naked Pansy Pakinson.  The equally naked figure of Draco Malfoy is just beyond Pansy.
Malfoy must have been shocked by the appearance of Professor Snape.  He stumbles, but he catches himself on Pansy.  He throws an arm over her shoulder and across her chest.  You get one guess what winds up in his hand.  He gets the expected reaction from pressing against a naked girl and grabbing a handful of her breast.  He's now as aroused as the rest of them.
Pansy remembers the Dark Mistress' admonishment.  She struggles along around her circle, dragging Malfoy with her.
The naked, erect boys with hands between the girls' legs shock the very up-tight professor.  The naked girls shock him more.  They're teasing the boys mercilessly and their wetness is running down their legs.  He commands them all to stop.  The chanting students are more afraid of the powerful Dark Mistress who treated them so roughly, twice now.  They don't stop.  Professor Snape makes a strategic withdrawal to seek help.
He returns in company with Professors Dumbledore and McGonagall.  The scene is even worse now.  The circles of students are now standing still because they can't walk.  They're paired off with hands on each others' genitals working each other over for all they're worth.  Some of the girls are gasping and trying to stand on buckling legs.  A few are screaming or moaning through orgasms.  More than a few boys are ejaculating and shooting semen all over their partner of the moment.  Draco Malfoy and Wilhelmina have Pansy between them.  Hermione wonders which one is holding her up.  Her limp form isn't standing by itself.
Hermione has been driven to handle herself a little by the sight of all that.  She's not shocked by it since it was her idea.  It just went far better than she expected.  The dark students had so much awe and fear of the Dark Mistress, they wouldn't stop even for Professor Snape.  Now the ones who have tormented her and her friends so much are caught at something more than embarrassing.
Professor McGonagall waves her wand and utters a curse that makes them all feel nothing.  All of them sit right down on the floor.  They all put hands and arms where they give at least a little modesty.
"So you still seek the powers and pleasures of the darkness?" she asks with a steely calm, quiet voice.
The students stare up at her.  They have no answer.
"There shall be more detention," the headmaster pronounces.  " For one week, you will spend the afternoon, supper time and evening in this room.  The detention will be supervised - by dementors from Azkaban prison!  Eat well at breakfast and lunch."
The students' hands leave the places they're covering.  They all cover their mouths or clutch at their throats.  This will not be a fun week. 
This is the moment Hermione chooses to leave for bed.  Her work here is done.
Saturday usually brings a weekend of relaxation, sports or study of what interests the students.  They rarely try to catch up on homework until late Sunday.  Hermione has told her close friends about the punishment the dark Slytherins face.  They try to listen to the conversation at the Slytherin table over lunch.
That's all bickering and blame.  They try to push it off on each other.  Most try to blame Malfoy.  The punishment is for all of them nonetheless.
Hermione, Ron, Harry and Cho are going for an outing right after they eat.  It seems that Hagrid is off delivering a young unicorn to Beauxbatons.  I'm sure that's his only interest there, aren't you?  Harry has the key to his house.  There are little creatures there to be fed and kept warm.
This isn't skulking, so nobody has any need for invisibility.  They do have need for warm trousers, sweaters and coats.  The coats come off straight away and Ron puts a log on the fire that has dwindled to a small glow.  The fire will be quite warm in just a few minutes.
These four know how to warm themselves in the meantime.  Cho wraps herself around Harry and starts the kissing.  Ron follows suit by lifting Hermione and holding her tightly to himself.  Yes, those are steamy enough to keep them warm.
The fire is soon warm and these four are hot.  They haven't said anything, but this is the outing Cho suggested.  They all have about the same expectation.  Cho suggests they all sit.  The painfully shy girl is going to do something the opposite of shy.
Hermoine snuggles on Ron's lap.  She puts his hands under her sweater and up to her chest while they watch Cho.  Cho, in turn, takes off her clothes slowly, one piece at a time and shows off what's revealed.  Her eyes are on Harry the whole time.  Ron and Hermione see her from the side.  She turns every now and then to show her back.  She struts with pride while she taking off her bra and panties.  These are her closest friends and they like to do the same things she does.  She's not ashamed in front of them.  She ends by pulling Harry from his chair.
Harry does much of the same and does it all for Cho.  Ron doesn't try to compete with Harry's physique.  He just puts Hermione's hand on his penis - his hard, straight penis.  Hermione smiles and kisses him.  The kiss doesn't last long.  Cho gets up, lets Harry sit and lands in his lap.  Hermione is next.  Cho pulls Harry's arms around her and puts his hands between her legs while Hermione strips.
Hermione does more of a dance.  She's out of her trousers and sweater quickly.  After that, she runs her hands around her body like she does in her catsuit.  She wriggles out of her bra and jiggles her breasts at Ron.  Her hands lift and squeeze those breasts as her hips wiggle and she does a little step.  She pushes her panties down slowly facing between the occupied chairs.  She gives everyone a good view.  Ron can't take his eyes from her, even when she wiggles in front of him and pulls him out of the chair.
Harry and Cho are hugging, kissing deeply and moaning already.  Only Hermione watches Ron strip.  She ends up panting with anticipation by the time his shorts slide down to reveal what she wants.
They're interrupted by a terrible sound.  The eerie shriek swoops right over the cottage.  They all know that sound from the year before last.  Those are the dementors.  The two naked couples scurry to the window.  They see four of the black, cold, ghostly figures swoop through the air.  Cho and Hermione snuggle to their lovers.  The boys stand behind the girls, wrap their arms around and they all watch out the window.
They see the dementors descend on the classroom where those dark students are doing their detention.  Perhaps the shock treatment of the dementors will drive the dark students to a different attitude.  Perhaps they'll get another taste of Azkaban later in life anyway.
Our four all shudder.  They've all felt the chill of those creatures and Harry has felt their kiss.  The chill lasts only as long as it takes these couples to get back to the comfortable chairs.  Their outing goes as planned after that.