Disclaimer: it's JKR's.

Physics Lessons

Hermione Flooed back to Headquarters before the meeting, landing neatly. Ron and Harry recognized the look of rabid excitement on her face.

"You've been to a library, haven't you," Ron said. "Got your book fix for the afternoon, have you?"

"No, Ronald," Hermione retorted. "I have not been to a library. I visited my parents."

Ginny looked amused as the boys exchanged dubious looks. "So how was the bookshop, then, Hermy?"

Hermione's nostrils flared in high irritation. "Hmpf." She turned on her heel, threw her hair over her shoulder and stalked off to her favorite armchair by the fire.

She pulled out a Muggle Physics textbook to read, pausing to make a few notes here and there, particularly on a section about energy and thermodynamics.

Realizing the room was empty, she climbed the stairs in search of her friends.

Hermione found them in the ballroom, practicing defensive hexes and dueling with Tonks and Lupin.

"Sorry to leave you alone down there," Ginny offered as they watched Ron and Harry, back to back, fending off their attackers while protecting each other. "You seemed pretty involved. You haven't missed much here, Tonks just showed us some moves she learned in Auror training. She's going to teach us those, too. Mum would probably call it Muggle dueling, but Tonks said it's called 'martial arts.' I guess doing strong magic takes a lot of energy, so the better shape we're in, the better our chances are."

Tonks stumbled and accidentally Stunned Lupin, so they decided to take a quick break and switch around a bit.

"Hermione and Ginny, feel up to taking on the boys?" Tonks grinned playfully.

"No way!" Ron protested, "I'm not fighting girls!"

"How about you and Hermione against me and Harry then?" Ginny suggested, eyebrows arched. "I know you have no compunctions about hexing me!"

"Ha!" Ron snorted. "Payback for those nasty messages you sent me! En garde!" He assumed a fencing stance.

Harry discovered, to his surprise, that he and Ginny made a very good team. Harry's quick Seeker reflexes and protective instincts meant he could throw out shields in a blink, while Ginny's stealth, accuracy and ruthlessness made her a deadly adversary. She hit Ron with a Body Bind curse, then while Hermione turned to help him, Ginny hit her with a Tickling Jinx.

Tonks and Lupin moved up to take Ron and Hermione's places. They endeavored to separate the two, but after several minutes the battle continued. Finally, Lupin used Levicorpus and had Harry struggling upside down. Ginny conjured a quick Shield and hoped Harry knew the counter charm to release himself. He was still casting spells while dangling from the ceiling, but his accuracy was impaired. As a last resort, he closed his eyes and conjured his Patronus.

"Hey, Professor, what happens if a Patronus catches you?" He grinned, directing his stag. Ginny quickly cast her own and sent it after Tonks. Tonks stumbled and Ginny's Patronus hit her, vaporizing as it collided.

Tonks froze as though hit by a Stunner. Lupin hastily dropped Harry from the ceiling, and Harry's Patronus faded away. Hermione and Lupin rushed to Tonks, swiftly checking her vital signs.

Ginny wrung her hands, apologizing profusely. Lupin reassured her that Tonks would be perfectly fine, she was just overwhelmed with joy at the moment.

"That must have been a good memory!" Remus smiled at her. "It takes a strong Patronus to knock somebody for a loop like this."

Ginny blushed. "Did she see the memory I used?"

"No, I don't think so." Remus winked. "If she did, you have my permission to Obliviate her. If it was that good, I don't want her to get jealous."

Harry cleared his throat. "So, Hermione, let's hear your book report for today."

"Oh that's right!" she gasped. "I need some help with an idea. Anyone familiar with physics?"

Harry shrugged, mumbling something about primary school, while Ginny and Ron looked puzzled. Lupin nodded.

"Well, we know Voldemort turns his nose up at anything Muggle, so I'm sure he never took time to understand the basic Muggle explanations for how the world works. Now we know that magic is a form of energy, right? The first law of thermodynamics says energy cannot be created or destroyed, only transferred or converted. Most importantly, living systems will break down unless they have some input of energy."

Hermine's eyes sparkled with excitement.

"Don't you see? If we can find out what a wizard's source of magical energy is, we can find a way to cut it off. 'The system will break down unless they have some input of energy'." She struggled to make them understand. "If we can stop the source of a wizard's magical energy, his system will break down, right? Harry, you don't have to kill Riddle if we can find something to stop his magical energy.

"Now I know we're training for battle here," she continued. "But we know the enemy doesn't fight fair. I think we need some new tactics, while we're looking for a key to magical energy. Let's create some spells that they won't know how to counter. I'm looking for a spell that converts magical energy, maybe using Muggle physics. Maybe we could find some American spell books, because let's face it, Voldemort probably considers himself so superior to American wizards that he would never stoop to learn any kind of counters to their spells. I know some of the ancient Native American wizards were extremely powerful, and we all know it's harder to block or counter spells you aren't familiar with."

Ron's eyes narrowed. "It's like Quidditch. The team with the best trained players and least predictable playing strategies will win every time."

"Oh, and Harry," Hermione turned to him, "I think the reason you got some of Riddle's powers is because his energy was expelled when your mum's spell rebounded on him. His energy passed through you, and transferred some to you. Parseltongue stuck because language synapses were forming in your brain at that age. It's hard to say what else may have stayed with you. That is a time of incredible brain growth and development in a child."

Harry nodded. "I wonder what the significance is now that he has my blood? My mum's blood protection kept him and Quirrell from even touching me when I was eleven, but in the cemetery after the Triwizard Tournament, he could, because he had used my blood for his body. In fact, he said it gave him the same protection. So is the blood protection at the Dursleys' still working? And what is the protection, exactly? Would it protect me from another Killing Curse? You're right, Hermione, I doubt that I could ever use that curse, even–or maybe especially–against Voldemort. I doubt I could cast it strong enough, and even if I could, it might not work against him, possibly even rebound on me."

He sighed, then smiled at Hermione. "You really are brilliant. I know you won't rest until you find a way–or probably several ways. Hey, what was that thing about combined poisons that Slughorn said? The sum is greater than the whole of its parts? That's like us. Individually, we couldn't do it, but together, we'll make the team that'll bring down that snake-faced bastard."

"Like the Sorting Hat and its unity speech," Ron nodded. "If the other three houses ganged up on Slytherin, they'd win."

"Erm, no, not exactly, Ron," Ginny said. "The Sorting Hat doesn't say Slytherin is always bad. It always mentions good qualities. I think it means finding good people from all houses."

"But the bad ones always come from Slytherin," Ron argued.

"You think Pettigrew was in Slytherin?" Harry queried. "I think anyone can give in to temptation or fear, regardless of house. That bloody hat wanted to put me in Slytherin. If I hadn't met you on the train, I wouldn't have known any better and might not have argued with it. Still, I'd like to think even if I had landed there, I'd still be me."

"It wanted to put me there too," Ginny whispered, eyes downcast. "Maybe because I had already started writing in the diary by then."

Harry reached for her hand, pulling her to his side firmly.

"I think being sorted into Slytherin is sort of a self-fulfilling prophesy," Hermione said. "They could be perfectly normal kids being sorted, but once they get in there, it's the way they're treated. People expect them to be mean and devious and spiteful, and everything they do is coloured by that perception. And think about the ones who grow up Slytherin. Like Malfoy, for instance. He's always been an arrogant berk, raised and trained to become a Slytherin Death Eater with no mercy. And yet when it came down to it… he couldn't hurt Professor Dumbledore when they were face-to-face. Imagine his punishment. I wonder if he's still alive... It's weird to feel sorry for him, but think of how he grew up, he never really had choices. They were made for him."

"Everyone has choices," Harry said stubbornly. "Sirius was raised the same way, but he didn't turn out like Malfoy."

"So you think we need the best qualities from all houses to make the best team?" Ginny asked, diverting the conversation to a safer topic. "Didn't you say the hat considered you for Ravenclaw?"

"Ginny would have to be the Hufflepuff," Ron smirked. "Loyalty is their thing, and Ginny's been loyal to Harry since she was about five. I'd have to be the Gryff, I don't fit anywhere else."

"That leaves me as the Slytherin," Harry said, "because of the Parseltongue thing, I guess."

They continued teasing each other as they all trooped downstairs where they found Fred and George emerging from the Floo.

Fred dropped to one knee and took Hermione's hand. "After seeing your communication devices, we've decided we are in love. Marry us, please," he begged. "Your intelligence is matched only by your beauty."

George shoved him over and eagerly took her hand, "Yes, marry us! Think of the possibilities!"

Hermione giggled and flushed. Ron snorted and pushed George over. "Shove off, you idiot savants. Your 'possibilities' would give her nightmares and have her committed to St. Mungo's long-term care ward."

"What's this?" Fred feigned outrage. "Have we competition for the object of our affections? Ickle Ronnikins, do we detect a note of jealousy, perchance?"

"Why Fred," George pretended to study their younger brother, "I believe you could be correct. Ronnikins has noticed that Hermione is, in fact, female. What think ye, Sherlock? Perhaps Ronnie would benefit from our sage advice and wisdom. Harry can join us."

"Elementary, my dear Watson," Fred agreed. He grabbed Ron while George grabbed Harry and dragged them off toward the kitchen.

Lupin asked Tonks to stay with the girls to rest from her Patronus collision while he set up for the meeting.

Tonks pulled both girls to a secluded corner and cast Muffliato to keep their conversation private.

"Listen, ladies," she began seriously. "I know these are desperate times, but that doesn't mean we can be irresponsible. Now you both know about contraceptive charms and potions, right?" Both girls flushed, and Hermione finally nodded.

"I, er, looked them up, just in case…" she whispered, embarrassed.

"It's nothing to be embarrassed about, you know," Tonks continued matter-of-factly. "It's a part of life and being a responsible adult. Now I imagine Molly wanted to have this little talk with you, Ginny, though maybe not for a few years, and probably not until just before your wedding night." She winked. "But sometimes these things are easier to talk about with an older sister type person. I know if times were different, you'd both be giggling about what to wear on your next Hogsmeade trip, but when we all know the hands on our clocks are pointed at 'Mortal Peril...' Well, priorities change."

The casual look on Tonks' face turned stony. "The other reason I mention it is more disturbing. There have been rumors that Voldemort may carry on some of Grindelwald's plans. Grindelwald captured young, pure-blood witches as 'broodmares' for his male followers. He called it 'species purification.' Word has been spreading, and with some well-timed articles in the Prophet, perhaps Voldemort will give up on that particular angle. It wouldn't be effective to waste his Death Eaters by capturing women who use a Chastity Belt charm, for example. The Prophet will be coming out with instructions for the charm, as well as other spells for basic self-defense."

The girls gaped at her, aghast.

Ginny recovered first. "What does the Chastity Belt charm do?"

"Well, it's sort of like applying the Fidelius charm to certain parts of your anatomy, but with a vicious burning hex built in as well," Tonks explained. "Definitely effective for warding off unwanted advances. The thing is, you will want to do the charm on yourself, because only the caster can cancel it. If someone else cast it on you and he or she died, it cannot be removed. It's even useless for them to attempt to torture women into removing it, as you have to be in the right, ah, mood to perform the counter charm. The Ministry thinks if it becomes common practice for all women to use it, the Death Eaters will stop kidnapping witches."

"Wouldn't most women rather just have a baby than fight?" Ginny asked. "A baby sounds better than torture and death."

Tonks regarded her carefully. "How do you think that baby would get in there, Gin? We're talking rape, you know. Forcible rape. Then imprisonment during pregnancy. I suppose pregnant women have to be treated somewhat better than their average prisoners, but I doubt it's a picnic in the park.

"Right, so then the babies are born. Do you think they would let them stay with mothers who might love them, regardless of method of conception? Not a chance. They won't allow any kind of influence like that. They would immediately take the babies away so the mother can be impregnated again. The babies would be raised on Growth Potion and trained as an army for Voldemort. Personally, I'd rather risk death than a life like that. I'll take my chances with the Chastity Belt charm. As a bonus, it protects the internal organs from most curses, like the Barren Curse that the Death Eaters have used on Muggleborn or half-blood women, or from someone else trying to cast the Chastity Charm on you. They don't want the 'wrong type' reproducing, you see."

Eyes wide with horror, both girls quickly mastered the spell, applying it immediately.

Tonks and the girls discussed various other methods of being responsible, which turned into a rather humorous discussion spanning the general topic.

"Harry is probably clueless, so Remus is going to talk to him. Anything he learned is most likely out of one of his roommates' smutty magazines. Poor kid, can you imagine how that conversation will go?"

"Remus could take Harry back to the Dursleys' tonight after the meeting to get the rest of his stuff and talk to him there," Ginny suggested. "Then he can tell the Dursleys 'good riddance' once and for all. If there's even a chance the blood protection is not effective anymore, he shouldn't stay there. Especially with Dumbledore gone. He never should have gone there at all." Ginny shook her head.

"Good plan," Tonks nodded, "I'll go help Remus… Why don't you ladies rescue your boyfriends and have a quick snack before the meeting starts." She winked. "Eat slowly though, I rather enjoy helping Remus…"

Ginny grinned at Hermione after Tonks left, then pulled two pair of Extendable Ears from her pocket. "Perhaps we should see just what our boys are learning, shall we?"

"Harry's going to have to be our resident Hufflepuff. You really should have been a Slytherin!"

Ginny just grinned and shushed her as they put the Ears against the door.

"Well, that was a waste of time," Ginny sighed. "We would have learned more by spying on Tonks and Professor Lupin upstairs."

Hermione snorted. "I think whatever they're doing up there would have melted these things right through the door."

Ginny's eyebrow arched in scornful disbelief. "C'mon, they're old! And Lupin? He's such a… professor!"

Hermione smiled, "Ahh, young Grasshopper, you have much to learn. Still waters run deep."

Ginny gave Hermione a dubious look. "Please tell me you're bragging about yourself and not about some deep, dark, personal knowledge you have about your former professor. Common fantasy, I've heard--that teacher-student thing--but honestly Hermykins, the ick factor there is through the roof. That may even be worse than my visual image of you and Ron in the shower."

Hermione sputtered, "What? Shower? We've never… We wouldn't… That's just… Hmmm…" Her gaze turned speculative.

"Ack! Stop that!" Ginny shrieked, laughing. "You're going to give me nightmares."

Hermione rolled her eyes. "Then stop calling me Hermy! Now, let's go Floo your mum and ask her to bring Crookshanks and the owls when she comes tonight. I need my furry little bedwarmer."

Ginny shuddered. "I said stop that, you sick, twisted perversion of womanhood. Oh, wait, did you mean Crookshanks? I thought you were talking about Ron… oof!"

Hermione elbowed Ginny in the ribs before tossing a bit of Floo powder into the fireplace. "The Burrow!"

Ginny giggled behind her. "Wait til I tell the twins about Hermy's little pet name for Ronnikins."