This chapter is where the story becomes a little bit AU, I suppose, because it's clear from the opening of Half-Blood Prince that Harry and Ron have no idea of anything (if there is anything at that point) between Lupin and Tonks then.
It's also where the story earns its M rating, so let's go full AU to make sure there is nothing inappropriate and assume that both Ron and Harry have had ther sixteenth birthday by this time.
"Ron," said Harry, after they'd been in bed trying to sleep for a few minutes.
"Yeah, mate?" Ron's voice was sleepy.
"Y'know that little firebolt Tonks gave me, have you seen it?"
"Dunno, Harry. You probably left it downstairs, that's where I left my Fitchett model." The model of the Chudley Canons' keeper on his broom had been Tonks' present to Ron, and he and Harry had spent the better part of the evening racing their models around the drawing room, with Hermione looking up over the rim of her book every so often and shaking her head indulgently, only muttering "For heaven's sake" when Ron deliberately steered his model to land directly on her head.
"You don't reckon Kreacher will chuck them away, do you?"
"Nah," Ron replied, yawning. "Haven't seen him all day, and he never does any cleaning if he can help it."
"Yeah, you're probably right," Harry said. After a long pause, he sat up. "Think I'll go and fetch it, though." Harry knew that really he was just avoiding the moment when, after Ron fell asleep, as he was enviably quick to do, he would be left alone in the dark with his thoughts, and worse, possibly his dreams.
With his instinct for doing the thing that Harry needed without knowing it, Ron sat up, too, with only a gentle groan. "Come on, then. I'll come too and we can swing by the kitchens." Only Ron could possibly be hungry on Christmas night, but Harry wasn't complaining. They shuffled their feet into slippers and crept out of the room towards the stair case, with only the light of a dim lumos from Harry's wand to illuminate them.
They had padded silently down the first flight of stairs and Harry had a foot on the top stair of the second flight down to the ground floor when a gentle pop made them freeze still as statues, and Harry muttered a very quiet nox. Lupin came quickly and silently out of the library into the hallway, and the warm light from the door he left open bathed the entrance hall, revealing Tonks standing in her cherry red coat with hair to match, clashing cheerfully with a green paper crown. Lupin grabbed her by the waist and pulled her close to him, away from the famous umbrella stand, before any misadventure could befall and Mrs Black be awoken.
"What's Tonks doing here?" asked Ron in a worried whisper. "D'you think it's something to do with Dad, or the snake?"
"I dunno, but it must be on Order business, why else would she be here? We might finally get the chance to hear something," Harry hissed in reply.
They missed the first snatches of Lupin and Tonks's conversation whilst they had this exchange, but it looked important, given how close together they were standing. Harry and Ron stood stock still in the dark, ears straining.
"Yeah, it was really nice," Tonks was saying in a low voice, as Lupin poiltely took her coat, "just the family. Way too much food, presents, mum doing Troilus and Cressida for charades and getting annoyed when we didn't guess it, that kind of thing."
"Can I get you a drink? Something to eat?" Lupin asked, quietly but loud enough for the boys to hear every word.
Tonks repressed a groan. "No, thanks, my mum really went to town with the Christmas dinner. I literally don't think I could fit anything else into my body at all."
"Not necessarily the news I was hoping for," Lupin observed, dryly, and Tonks stifled a spurt of laughter.
In the dark, Ron and Harry could feel rather than see each other's looks of confusion. What was so funny about that, and why were they acting like this was a social call?
"Shall we?" Tonks said, heading towards the stairs. She held out her hand to Lupin. Harry and Ron shrank back into the bannister, hardly daring to breathe. There was no way they wouldn't be discovered, but what on earth could Tonks possibly want upstairs? Maybe she was here to see Sirius - but why did she think Lupin needed a hand? He looked pale and worn, but no more so than usual, and he was clearly quite capable of going up the stairs.
"I'll just fetch your present, it's in the library," Lupin said.
"Oooh, let me have it now. I've got yours, too," Tonks said, excitedly, abandoning the stairs and following him into the room. She shut the door behind her and Ron and Harry breathed deep sighs of relief.
"What's all that about, then?" Ron wondered, as Harry re-lumos'd his wand and they resumed their tip toeing down the stairs.
"Dunno," Harry muttered. It had almost seemed as though they were - but, no, that was clearly ridiculous. He and Ron crept extremely carefully across the tiled hallway and into the drawing room, retrieved their figures, and padded out into the hall again. Harry turned to the stairs, but Ron was making for the kitchen.
"Come on," Ron said, "let's grab a mince pie or two."
Harry followed dutifully, although not being cursed with Ron's hollow legs, like Tonks he couldn't imagine being able to eat anything. They made short work of gathering provisions in the kitchen and then made for the dark, narrow back stairs which led off kitchen up to the upper floors and had clearly been designed for use by house-elves. Still cautiously, they opened the door to the dark staircase and started to creep up the narrow stairs in single file. Four stairs up the staircase twisted around a corner. And reaching this point, Harry froze again, causing Ron to walk straight into him.
"Shhhhh," Harry breathed, in anguish, as Ron opened his mouth to complain. "Look!"
The stairs gave on to a wide serving hatch into the library, presumably intended so that elves could pass large trays laden with decanters of brandy to the master of the house without disturbing him. The serving hatch had been stuck open since at least the summer, and possibly a long time before that, but nobody had bothered to fix it. The other challenges that the house presented, such as doxies and ghouls, had seemed much more pressing. Now, however, it served to give the boys a televsion screen-sized view into the softly-lit library and what was going on inside it.
Ron's mouth fell open. After a while, he mumbled, "I might be wrong, but I really don't think that's Order business."
Lupin and Tonks were kissing passionately, and Lupin's left hand seemed to be somewhere up Tonks's top, while his right hand supported her back. Tonks, leaning back slightly under the force of Lupin's kiss, had lost her paper crown and had the fabric of his faded grey shirt bunched in her firsts and she seemed to be trying to pull him even closer to her. When they finally tore apart, Lupin was actually panting, and Tonks laid her hand on his arm to steady herself. Then she wound the fingers of her right hand into Lupin's hair and with the other pushed his old brown jacket off his shoulders and onto thr floor. When he spoke, Lupin's voice was deeper than usual, hoarse with desire. "We need to go upstairs."
"Not a chance," Tonks murmured, unbuttoning Lupin's shirt as she kissed his neck, "we're neither of us in a state to apparate and I can't walk up those stairs quietly at the best of times." Lupin's hands were back on her body, and he moaned into her hair. They staggered back clumsily onto the long leather sofa, and he pulled her skirt up to her waist, growling "please, please," as he ripped off her knickers and pushed her legs apart. Tonks's breath hitched and she opened her legs to Lupin, whose hand they couldn't see but was definitely doing something in that area.
"All right, we definitely shouldn't be watching this," whispered Harry, although his whole body felt like it was on fire and he stared transfixed as Lupin kissed the insides of Tonks's thigh, still doing whatever it was he was doing with his hand.
"No, we shouldn't," agreed Ron. There was a long pause. Then he said "Oh, right," and, seeming to come back to himself, he turned silently to go back up the stairs. Harry was still on the stair above him and he didn't move as quickly as Ron, with the inevitable result that Ron crashed into Harry with a bump. Again, they froze.
Tonks sat up sharply, whipping her wand out from her stocking. Remus sat back on his legs, too, scanning the corners of the room and looking towards the pitch black well of the serving hatch.
"Just the noises that houses make when they're old and creepy as hell," Tonks gave an uncharacteristically breathless laugh. But she flicked her wand towards the door and the serving hatch. "If anyone passes the top stair on either staircase, we'll hear a ringing and they'll be floodlit," she said. "Auror spell for securing an area."
"Perfect," Lupin said approvingly, with a hint of the professorial tone that Harry and Ron remembered from third year. But then he kissed Tonks's shoulder in a distinctly unprofessorial manner, and groaned quietly as she twisted around and sucked gently on his earlobe.
"Do you mean my wand work?", she asked, laughing softly as she released him and his hand came up to softly stroke her face.
"I mean everything," Lupin replied. He smiled tenderly, and in the soft light of the room he looked younger and more carefree than the boys had ever seen him. He mumbled something else, but they didn't catch the words, primarily because he'd removed Tonks's jumper, struggled briefly with her bra and lowered his head to her breasts, kissing and nipping and sucking, while she moaned underneath him and ran her hands across his back, pulling off his shirt to reveal his back, taut, scarred and pale.
Neither Harry or Ron could move, and Ron mumbled in quiet astonishment, "Blimey, she seems to be just as into it as him." Ron wondered how a girl - that girl of his fantasy who always ended up looking exactly like Hermione, no matter how she started off - would react to him doing the same things. Next to him, he could hear Harry swallow.
Tonks proved him right the next moment by arching her back with pleasure and frustration and half sitting up and reaching for Lupin's belt. Lupin gave her right nipple a final nip and looked at her, grinning.
Tonks undid his belt buckle nimbly, but before she could get any further, Lupin had deftly slid off the sofa and was kneeling on the floor.
"Bloody hell, he's going to propose," Ron whispered.
"I don't think -" Harry began in reply, but his hushed voice trailed off as it became very clear to both of them what Lupin was doing, and it didn't involve words.
There was no pleading this time. Lupin gently pushed Tonks's legs apart again and brought his mouth to her. She gasped with pleasure and Harry and Ron, though each could see only the barest outline of the other, looked at each other in amazement.
"Fuck, Remus," Tonks hissed, pulling on Lupin's hair in a way that Ron felt sure must have hurt him, but he didn't stop. Whatever Lupin was doing - and Ron wished he could see, because this struck him as a massively useful and enjoyable skill - Tonks seemed to like it even better than what he'd been doing before with his hand, because she had to cram her fist against her mouth to stop herself screaming out. Lupin's hand was still there, too, Ron realised and he frowned slightly. How many things were there to do down there? The magazines he'd "borrowed" from Fred and George hadn't given a lot of information on female pleasure and it was all a bit mistifying. But if, in some far off hypothetical future where he actually had the balls to tell Hermione how he felt and she didn't hex him into next Tuesday, he could find a way to make her moan and thrash her head in ecstasy like that, then he definitely wanted to learn.
"Remus," Tonks choked out, her head back, and then her body crumpled and went still. Lupin, looking incredibly pleased with himself, immediately stood up and almost scooped her into his arms so that she half-sat and half-lay across him on the sofa. He again murmured fy nghariad, which Ron assumed was some kind of spell (a sex spell, maybe?), gently kissed her eyes and wrapped his arms tighter around her. Ron wasn't sure what to make of the fact that he could have sworn he saw Lupin lick his fingers as he cradled Tonks to him. Was that a werewolf thing? Or something that anyone could do in a similar situation?
Ron and Harry both relaxed slightly, assuming that the interlude was now over and Tonks and Lupin, once they'd had a moment to recover, would apparate upstairs any minute. A few minutes was enough to show them how naive they'd been, however. The gentle, lazy careses that Lupin and Tonks had been sharing gradually gathered heat and momentum again, and Tonks had twisted around on Lupin's lap, wriggled his trousers down and was slowly but firmly stroking his cock while Lupin emitted guttural groans, quite unlike his usual mild speaking voice, and gripped onto her shoulder. Lupin suddenly gave a very sharp intake of breath and sat up, kicking off his trousers and boxers, so that Tonks was straddling his lap, staring into his eyes in a frenzy of what looked like love and pleasure.
"I should warn you, I'm not going to last very long," Lupin said, his voice sounding strained. "How do you want it?"
"Hard and fast now. Soft and slow later," Tonks replied decisively, and she ran her tongue up Lupin's throat, from his collar bone up to the base of his chin. Ron barely had time to be impressed at anyone being able to offer different styles of sex, like a menu at a cafe - he was far from sure that he would know how to deliver even one - before Lupin had pulled Tonks down onto him in a swift, firm movement, and with a gasp she threw her head back, and then lifted herself half off him and he did it again, faster and then again. They crashed together repeatedly with the violence of waves breaking on a storm-swept beach and Ron wouldn't admit it even to himself, but he was slightly shocked at how rough it looked. He'd always imagined himself being more, well, romantic in this situation, but there was absolutely no doubt that this was exactly what Tonks wanted. Ron filed that away to ponder on later.
Suddenly Lupin breathed in sharply, and held still. Tonks held still too, and then Lupin laughed shakily, and said, mysteriously to Ron, "Just in time. Give me a moment". Tonks raked her fingers through his hair, kissed his forehead and then manoeuvred herself off him with uncharacteristic grace. Lupin stood up and stayed still, panting, for a few seconds and then he took her in his arms again. They kissed slowly at first, but once again the heat gathered quickly and very soon Tonks was lying on the sofa and he was on top of her. He looked down at her, his eyes dark and tender. "All right?", he asked breathlessly, and in a voice rich with unspeakable devotion. "Never better," Tonks replied. He thrust into her, suddenly, and Ron wasn't sure whether to interpret the noise she made as one of agony or ecstasy. Lupin thrust again and again, harder and harder like he was trying to reach through to her heart, and Tonks rose her hips up to meet him, gasping louder with each thrust. She hooked a leg over his shoulder and Lupin must have known what the effect would be because he quickly put his hand over her mouth before he thrust again, stifling a scream that would certainly otherwise have woken anyone on the first floor. Lupin's other hand was braced on the arm of the leather sofa, the anchor keeping their balance on a narrow piece of furniture not designed for these kinds of activities. It looked incredibly uncomfortable, but Lupin didn't even seem to notice, and Ron couldn't blame him.
"God, Dora," Lupin cried out, then in a voice which was quieter, but sounded a bit strangled, as he regained some vestiges of control, "I can't -"
He didn't finish his sentence, because a few seconds after he had cried out her name Tonks moaned deeply into Lupin's hand. She went tense all over and opened her eyes, and Lupin followed her immediately with a stifled cry which didn't sound like any language at all. Then time stilled and they lay together, limbs entwined, as their breathing slowly returned to a normal pace. Moving at last with a deep sigh, Lupin kissed Tonks very gently under her left eye, and Ron saw that he had been wrong; what he had witnessed, carnal and frantic as it may have been, had somehow also been extremely romantic.
Lupin got up, flexed his fingers experimentally and, looking at Tonks affectionately said in tones of mild surprise, "Dora, you bit my hand." He retrieved his wand from his trouser pocket and mutttered a spell. Ron did know about this one from Fred and George - it was the spelling for cleaning up in the aftermath of sex. He was reassured to have heard Lupin use it, because he'd been haunted by the suspicion that his brothers had told him it wrong, just for laughs. Mind you, at the rate he was going he'd probably be about 100 before he ever needed it, he told himself, glumly.
Tonks stretched lazily and grinned. "You shouldn't make me scream if you can't take the consequences. Next time I'll try to remember the silencing charm," she replied.
She sat up, and in doing so, fell off the sofa. Lupin, who was putting his trousers on with careful precision, turned to her with a practiced solicititude, and they both chuckled gently as he helped her up. She kissed his scarred shoulder casually as he handed her her clothes, of which she put on only her skirt and boots, slipping her arms into his discarded shirt instead of her jumper. She gathered the rest of her things in a messy bundle in her hands. There was something so domestic and so intimate about the way they dressed, the brief, unnecessary touches, the easy companionship of it, that Ron suddenly felt ashamed, for the first time since Tonks had closed off their exit, for intruding on their privacy. Lupin shrugged on his faded jacket, and Tonks picked her crumpled paper crown off the floor and set it on his head.
"Suits you," she said. "Adds to your sexy gravitas."
Lupin raised an eyebrow but left the hat on his head, and he picked up a couple of packages from the writing desk. "And to think that we still haven't got around to opening these," he said, softly. Tonks reached to take the smaller package from his hands, but he swung it high out of her reach.
"Let's go upstairs," he smiled and apparated with the softest of pops. Tonks mumbled something, flicked her wand towards the doorway and followed immediately after.
"D'you think she's just undone that spell to secure the area?" Ron asked Harry after a few seconds, his voice still a whisper although the need for secrecy had diminished.
"Only one way to find out," replied Harry and he strode firmly on up to the top step. Blessed silence greeted their crossing of the threshold and they scurried up another floor and all the way back to their room.
It was almost pitch black back in the bedroom, which was just as well because, as they scrambled back into bed, Harry and Ron were both sure that they were too embarrassed to ever meet each other's eyes again.
"Well. That was ... weird." Ron said, finally, lying in his bed waiting for his blankets to absorb his heat and warm up, and staring up into the blackness.
"So weird," agreed Harry, fervently.
"But also ...really hot?" Ron's voice was tentative.
"So hot," Harry agreed. "Insanely hot." Then they both started laughing, in a sudden burst that had nothing to do with humour and everything to do with releasing the tension of the last twenty five minutes.
"Who's have thought it," Ron mused, as their laughter died down. "Professor Lupin. And Tonks! She's so cool and fit and he's- well, professor Lupin. And she really seemed to be into him."
"She definitely seemed very into what he was doing," Harry agreed, and they laughed again.
"Y'know, I think maybe we shouldn't tell anyone about this," Harry said, after a pause.
"Really? That's a shame because I was planning on giving mum a blow by blow description over breakfast tomorrow," Ron retorted. He could have sworn that he could hear Harry rolling his eyes in response.
"You know what I mean, that they're.. well, together. It doesn't seem like they want anyone to know."
"Maybe everyone else does know, mate. She's here for breakfast a lot of the time. I thought she was just like me, never turn down a decent breakfast, but I dunno..."
"Oh. No, Lupin would've told us if people knew."
"D'you think? I can't quite imagine him sitting us down and saying, 'Now, boys, just so you know, I'm shagging Tonks six times sideways every time I see her.'" They both laughed and then in a different tone Ron said, "I remember Dad saying that there's been talk at the Ministry about new laws, even worse than the ones that bitch Umbridge already introduced, making it illegal for anyone to associate with dark creatures like werewolves. There's opposition to it, but there's a lot of support, too."
"Do you remember the outcry at school when people found out? People who he'd been so kind to were up in arms about how awful it was to have him anywhere near them." Harry spoke quite savagely, remembering Lupin's pale, resigned face as he'd packed his trunk.
"I guess if it got about that Tonks was shacked up with a werewolf, her job at the Ministry..." Ron trailed off and they lay in somber silence. Then, more cheerfully, he said. "Right, we won't let on to anyone that we know they're together. Saves having to come up with a story for how we know, anyway, because I'll be taking tonight to my grave."
"Wild hippogriffs couldn't drag it out of me," Harry agreed. "Tell you what, though. They seemed really happy, didn't they?"
"I'd be pretty bloody happy if I was doing that with H - I mean, if I was doing that," Ron replied, recovering from the slip and thanking his stars - not for the first time - that his friend was so spectacularly oblivious. Then, smiling, he added, "But I know what you mean. And yeah, they did."
Silence reigned for a while and then Ron said "'Night, mate." He still fell asleep relatively easily but the fact that he forgot to eat the mince pies they'd extracted from the kitchen at such a memorable cost told Harry that he must certainly have been quite profoundly distracted by what they'd seen.
As for Harry, he stayed awake for a long while, but his thoughts and eventually his dreams were certainly not the dark ones that he had foreseen earlier that night.