Disclaimer: All Harry Potter characters herein are the property of J.K. Rowling and Bloomsbury/Scholastic. No copyright infringement is intended.
Author's Notes: Huge thanks to my last-minute betas, r and b, and to the plot bunnies that allowed me to write my first Sirius!fic. Ariadne, I hope you enjoy, and that this relationship is screwed-up enough for you!

Mr Potter is Entirely Complicit

All it took was one good smack across the face to bring Sirius Black back to consciousness. Severus would have rather liked to try another couple of swipes, but restrained himself. If all went as planned, he would need his strength.

Looking around somewhat blearily, Sirius did his best to quickly assess the situation. Much as he hated to admit it, this wasn't the first time he had been knocked unconscious and woken in a strange room. But the odd thing was that this room wasn't strange. He couldn't mistake the dingy wall paper, moth-eaten furniture and musty smell of his own room. When he stopped to listen carefully, he could even hear Buckbeak moving around on the floor above. Nor could he mistake the large nose and greasy hair of his would-be captor, and his face contorted with rage. "What the fuck do you think you're—"

"It's okay, Sirius," said an equally familiar voice. Sirius shifted his focus, and saw Harry sitting on the bed, dark clothing helping him blending him to into the shadows.

It was worse than he'd feared. Snape had captured them both, had shown his true colours at last. Voldemort was probably on his way at that very moment, would burst the door down and murder Harry right in front of him. Sirius reached for his wand (surprised to find himself quite free to move), but it had been removed.

Snape, however, wasn't paying him the blindest bit of attention. "Potter, I thought we had agreed on silence." When Sirius looked up, Harry looked strangely remorseful. When had Harry ever looked remorseful for disobeying Snape? Surely glee was the order of the day? Snape sighed in that queen-y, melodramatic way that James always used to mimic at school. "Disrobe and assume the position."

Sirius' eyes widened, and he drew breath to protest, but Snape was too fast for him. "Silencio!" he said, with a too-casual flick of his wand. A smug smile settled on his face, as Sirius began to move his mouth, releasing nothing but silent air. "Much better," he muttered, "Perhaps now you'll be able to listen a little better."

Behind Snape, Harry was removing his clothes. He was already down to his boxers. He must be under some sort of Imperio, or— "Ah-ah," Snape smoothly shifted in front of Sirius, blocking his view of Harry. "Listen. I imagine you're expecting some hoard of Death Eaters to burst in and ravage your beloved godson—" a soft whimper from Harry, and who could blame him? "—before murdering him right before your eyes? As in most cases, you would be decidedly wrong. I have noticed, during my perusal of Harry's mind over the last few weeks, that you have not been a very positive influence on his development."

Sirius moved his mouth, trying to protest that he had done nothing of the kind, that he wanted Harry protected as much as anyone, that he had agreed to the whole stupid idea in the first place. But, of course, nothing came out.

"Letters describing me as a fraud or a quack. Floo discussions relating my sordid past – which, I might add, is nobody's business but my own. How, Black, am I expected to teach a boy, who is told by his only relation that he doesn't really need to learn, and especially not from me?" Severus paused, leaving Sirius to wallow in a stubborn, mutinous silence.

Stepping aside, Snape revealed Harry. Young Potter was stark naked with his back to the two older men, bent at the waist with his hands braced on his knees. Snape smirked in appreciation at the way Harry's arse looked, all chiselled Quidditch muscles, the cheeks slightly spread, hinting at the puckered entrance within. Turning, Snape used his momentum to land a sharp, flat-palmed slap on Potter's right buttock. The contact was hard enough to make Harry stagger slightly, and left a red mark on the otherwise perfectly pale flesh. Sirius jumped up in protest, but Snape didn't even bother to look at him as he said, "Don't make me restrain you, Black. I can assure you, Mr Potter is entirely complicit in these games."

One of Snape's stained, long-fingered hands rested on Potter's spine, fingertips playing over the stuck-out vertebrae. "The mind is an unusual thing, Black. I wouldn't expect you to understand. I'd hardly say what resides in your cranium passes for a mind. I am attempting to teach Harry to close it off completely. But in truth, there are many facets to the mind. Thoughts, memories, ideas, opinions...dreams." His mouth twisted in what might, on any other man, have been a smile. "When I discovered the nature of Mr Potter's dreams, I couldn't help but assist him in actuating them."

From the bed, Snape took a long, thin stick of birch, and twirled it idly in his fingers as he spoke. "Harry's problem is that he is surrounded by people under the impression that he is a child doing a man's job. Even a glance through his mind would tell you that he is a man, unfortunate enough to still be encased in a...younger body. Would you concur, Mr Potter?"

Sirius' eyes flew to Harry's face, which he could see hanging between his bare legs. He nodded twice, green eyes trained with hungry anticipation on Snape. Sirius was more than disconcerted to note that Harry's cock was hard.

"Harry – on the rare occasions I allow him to open his mouth for anything other than the most pleasurable exercises – has expressed concern that you will find a way to discontinue our," that was most definitely a smile, "lessons."

With lazy flicks of the birch, Snape began to tap the thin stick against the lower swell of Harry's arse. "He wants me to make sure you understand." The thwacks were quick, and became louder as Snape spoke. "I explained I am a man of talent, though I can only do so much. It isn't easy explaining anything complex to a man who learned to transform into a dog to lick his own bollocks."

Snape tapped his wand against Harry's knee, and from its tip sprung a green cord, which wrapped itself sinuously around Harry's wrists and legs, binding him in his bent position. "Twenty strikes today?" he asked Harry casually. Sirius' eyes were wide, as he watched Harry bite his lip, cock bobbing, before he nodded enthusiastically. "Perhaps you could keep count, in case twenty is a little high for your godfather to keep up." To Sirius' mortification, he saw Harry's balls twitch.

In a single, clean stroke, the birch arched through the air, landing with a resounding thwack on the tops of Harry's thighs. Harry let out a gasp, gulping air in to sob, "One, Professor." As Snape pulled the birch back, Sirius saw that it left a clean pink stripe marring the creamy flesh.

With a sick sinking of his stomach, he noted that his own body was responding to the sight. With Harry bent over like that, he could almost be any man – he could almost be James – bent in half, with his most delectable portions offered up, purely for his benefit. Trying not to draw attention to himself, he crossed his legs slowly, hoping the hard denim of his jeans would mask his burgeoning erection.

"Two, Professor," Harry whispered as the second blow fell higher on his arse. Then, quickly, "Three, Professor!"

"Are you quite all right, Black, or can I offer you some assistance?" Severus remarked, turning on his former classmate with a scowl, as though he had been interrupted in the middle of a lecture.

Sirius opened his mouth to respond, remembered he couldn't, and quickly shook his head. But as the fourth and fifth blows landed on the round of Harry's backside, Sirius found it increasingly difficult to hide his entirely inappropriate appreciation of his godson's 'punishment'.

"Oh! Six, Professor," Harry was moaning, now. There was a thickening to his voice that made it almost unrecognisable. And Sirius told himself that he could not help it if his hand shifted against the hard bulge in his jeans, nor the way his breathing had become shallow, nor the fact that he could no longer bear to look away from the strawberry-pink stripes that criss-crossed Harry's muscular buttocks.

Seven. Eight. Nine. Ten.

And so distracted was Sirius, that he did not notice for fully twenty seconds that Snape had stopped the previously swift strikes. He was, in fact, looming over Sirius, hands on hips, eyebrow raised and an intrigued expression on his face. "Potter, I think your godfather needs some assistance."

There was a sharp in-take of breath before Sirius tried very hard to argue. Severus was one step ahead, however, and had levitated Harry and turned him around before Sirius could even think of the possibility that he could get up and leave. But then, Harry's face was in his lap, his green eyes looking up at him with a lascivious, hungry twinkle. Sirius' breath escaped in a sigh, and of their own volition, his hands opened his fly and, with some relief, drew out the hard length of his cock.

"I think," Severus said softly, landing another smack on Harry's arse, "the mongrel is starting to get the idea."

"Eleven, Professor. Yes, sir." That was all the suggestion it took. Sirius tried very hard not to think about how many times Harry had been in this position, how precisely he had learned to tilt his head to swallow a cock at that angle. And then Sirius couldn't think anymore, because all that mattered was the sweet suction and searing heat of Harry's mouth on his prick.

"So beautiful," he heard Snape mutter, barely audible. The strangeness of it registered briefly in Sirius' mind, but it wasn't nearly as important as the impulse to wind his fingers in Harry's hair as his head bobbed up and down. "For possibly the first time in history, a Potter has earned a reprieve."

When Sirius' heavy-lidded eyes rose up, Severus had also bent down, his attention on Harry's arse. And he could tell the precise moment Snape's tongue found Harry's entrance, because of the strangled moan that vibrated around his cock, making him dig his fingernails hard into Harry's scalp. But that just made Harry suck harder, made him scrape teeth and swirl his tongue, until Sirius was nothing but a melted pool of nerve endings.

"Shall I fuck you, boy?" Snape asked, slightly muffled between Harry's arse cheeks. "Shall I slide into you while your mouth is tight around your godfather's cock?"

The only response Harry could make was a muffled sound somewhere between a moan and a groan, that Sirius felt reverberate through every fibre of his being. Sirius closed his eyes so he could not see the expression on Snape's face as he made good on his offer.

All he knew was the sudden, urgent yelp Harry gave, at the moment that must have been when Snape breached his hole. That was all it took for Sirius, who howled and came hard into Harry's mouth. He was certain Snape was smirking at him, but it didn't matter. All he felt was the softness of Harry's hair under his hand, as he ran his fingers through the tangled mess and watched stars explode in the black of his closed eyelids.

Sirius tried to keep his eyes closed, but could not resist watching their writhing, pale bodies. He tried hard to fight the tingles of arousal that skittered across his skin as he listened to his hated classmate and his best friend's kid as they made love. Their sex was violent. They grunted and whined and hissed; they bit down on one another and clawed, their flesh smacking together. But it was making love, nonetheless. And Sirius was disgusted at the way his body reacted, a half-erection burgeoning once more, as Harry called out some strangled name that could have been 'Severus' or could have been 'Sirius', and Snape growled low in his throat as his thrusting body reached its climax.

Only when there was silence – or near-silence – once more, could Sirius open his eyes. He swallowed hard at the sight of the two panting men, one slumped over the other in pleasurable exhaustion. As though forgetting he was being watched, Snape ran his hands back up Harry's arms, and planted a dry kiss on his shoulder, covering a large dark mark where he had obviously bit down only a few moments earlier. When his dark eyes rose to Sirius, he was quick to pull away from Harry, only the lingering brush of his fingertips belying the merest hint of any tenderness between them.

Harry himself was close to collapsing, and it seemed only natural to Sirius to reach out for him, and pull Harry onto his lap. He was sticky with sweat and come, and his breath was hot and damp against Sirius' neck as his body returned itself to normal. "I'm sorry," Harry muttered against his godfather's shoulder.

"What for?" Sirius asked, eyes flicking up to Snape. But the other man had his back turned, was preoccupied with re-establishing his veneer of prickly self-protection.

"For disappointing you."

"I'm not disappointed," Sirius lied softly, and ignored Snape's crude snort. "But you could have found a more tactful way of telling me."

Harry sat up and smiled. He was messy, dirty, beautiful. "That was Professor Snape's idea. I think it worked all right, really."

"Do forgive my breaking in on your afterglow of sentimentality," Snape interjected, the sneering, greasy, arrogant arse once more. "But Mr Potter must be returned to Hogwarts before he is missed."

"Yes, Professor," Harry said, with the slightest tone of mocking in his voice now that the game was over. He slid from Sirius' lap, and began the hunt for his clothes, pulling them on hastily as Snape advanced on his godfather.

"Can I assume we are clear now? There will be no more interference with my lessons?" he asked.

"As long as you're teaching him how to stay alive as well as how to suck cock," Sirius said pointedly, glancing at Harry who made a very good show of paying them no attention, "then I won't interfere."

Snape nodded curtly before turning back to Harry. "Come, Potter," he said, striding from the room without looking back. Harry took a moment to look back and smile at Sirius, raising a single hand in a half-hearted wave, before following the Potions Master from the room.

Sirius could hear their footsteps, as they made their way down the stairs. Snape's were crisp and even, purposeful. Harry's were rushed, as though he took the steps two at a time, and he made no effort to muffle his heavy, uneven tread. Raking a hand through his hair, Sirius took a deep breath and resigned himself to the knowledge that nothing was ever easy.