Chapter 1
1. The Time James Stole Regulu's Cat
(Betrayal, Bribery, and Why You Should Never Trust a Feline with a Gryffindor)
Regulus Black had not planned on spending the first hour of his journey back to Hogwarts searching the train for a disloyal little beast.
Yet here he was, weaving through crowded compartments, his patience wearing dangerously thin as students pressed past him, their voices a muddled hum of laughter and chatter.
He adjusted his grip on his wand, fingers twitching at his side. If anyone had so much as touched his cat, they were getting hexed into next week.
“I knew I should have left you in your carrier,” he muttered under his breath, scanning the corridor.
His cat, of course, had never been particularly obedient. Of all the creatures in the world, of course Regulus had ended up with one that did exactly as it pleased, whenever it pleased. It had probably wandered into someone’s cabin and made itself at home, wholly indifferent to the fact that it belonged to him.
And Regulus did not like losing things.
He turned another corner, irritation simmering beneath his skin, when a familiar voice—loud, obnoxious, and unmistakably Potter —cut through the train’s background noise.
“You’ve got expensive taste, mate,” Potter was saying. “Bet you belong to some posh twat, don’t you?”
Regulus stopped dead.
His fingers curled into fists at his sides as he stepped toward the half-open cabin door, already knowing exactly what he was going to find.
And there it was.
His cat—his traitorous, disloyal cat—was curled up comfortably on James Potter’s lap, purring like it had just found the best seat on the entire train.
Regulus inhaled sharply, pushing down the urge to curse Potter on sight.
Potter was leaned back against the seat, his legs stretched out like he owned the entire bloody compartment. He had one arm draped over the backrest, the other idly scratching behind the cat’s ears—like he had any right.
Regulus didn’t miss the half-eaten Pumpkin Pastie on the seat beside him.
“Unbelievable,” Regulus muttered.
As if sensing his presence, the cat flicked its tail and turned its head lazily toward the door. Potter must have followed its gaze because a second later, he tilted his head back, hazel eyes meeting Regulus’s.
He did not wait for him to speak.
“That’s my cat.”
Potter blinked. Then, as if only now realizing the situation, he glanced down at the cat sprawled across his lap, its head now resting against his knee like it had never known another home.
A slow, insufferable grin spread across Potter’s face.
“Oh,” he said, far too casual. He stroked the cat’s head again, like it was his. Regulus’s fingers twitched against his wand. “Didn’t know you had a cat, Black. But I guess that explains why he’s got a bit of an attitude.”
Regulus inhaled slowly through his nose, willing himself to not commit a crime in broad daylight.
Mostly because he was trying to decide whether to hex James Potter first and retrieve his cat later, or retrieve his cat first and then hex James Potter into the next century.
James, for his part, looked far too relaxed for someone who had just committed theft.
“Right,” he said, shifting slightly, as if only just now realizing that Regulus was not, in fact, amused. “So, funny story—”
Regulus arched an eyebrow.
James hesitated. “Or, er, not funny. Depends on your perspective, I suppose.”
Regulus crossed his arms. His silence was practiced—sharp and expectant, just like Mother taught him.
James, however, was clearly immune to social cues because he continued, undeterred:
“So, I was at the trolley, yeah? Buying sweets, minding my own business, when this little guy just walks right up to me—bold as anything—and decides I’m his new best mate. I even tried to send him away! Told him to go find his owner and everything.” James gestured at the cat, who was still comfortably draped across his lap, purring like the traitor it was. “But he just kept following me. Practically forced me to take him in.”
Regulus narrowed his eyes.
James grinned. “Which, I think, technically makes this his fault. Not mine.”
Regulus inhaled slowly through his nose. “You fed him, didn’t you?”
James blinked. “...I mean, yes, but—”
Regulus exhaled sharply.
Of course.
This wasn’t theft. It was bribery.
And, naturally, his cat had zero loyalty when it came to food.
James seemed to take his silence as some kind of victory because he leaned back again, stretching.
“So, no harm done, right? You’ve got your cat, I’ve got all my limbs, no hexes necessary.”
Regulus stared.
James stared back, still looking far too pleased with himself.
Regulus reached for his wand once again, but before he could do much as lift it, the compartment door slid open again—this time with much more force.
“Oi! James!”
The voice was loud, brash, and far too familiar.
And then—like a bloody hurricane—Sirius swept into the room, all wind-tossed hair and reckless energy, a cocky grin already in place, like he owned the world and knew it.
Regulus’s fingers twitched at his side. He had the sudden, violent urge to leave.
Lupin and Pettigrew followed more calmly, though Lupin looked vaguely exasperated, like he had already resigned himself to whatever disaster was about to unfold.
“There you are—thought we lost you! What the hell took you so—”
And then Sirius stopped.
His storm-grey eyes locked on Regulus immediately.
For a fraction of a second—so brief it could have been imagined—his grin faltered. Something unreadable flickered across his face. But it was gone before Regulus could name it, wiped away like a mistake on parchment.
Sirius’s lips curled. Sharp. Mocking.
“Well, well, well.” He crossed his arms, leaning deliberately against the doorframe, blocking Regulus’s only way out. “Look what we have here. Baby brother, out of his cave. That’s new.”
Regulus bristled. The words were light, flippant—but the edge was there, hidden beneath the laughter. Sirius’s smirk didn’t slip, but there was a flicker of something in his eyes—not hesitation, exactly. More like confusion, quickly masked by his usual arrogance.
Sirius tilted his head, eyes glinting with amusement. “What’s this, then?” His voice was light as he gestured between Regulus and James with a lazy flick of his wrist. “Didn’t think you two were on speaking terms.” His smirk widened, sharp as a knife. “Planning a dramatic betrayal, little brother? Or just expanding your social circle?”
“Enough. Give me my cat back, Potter.”
Sirius’s gaze dropped, finally registering the deeply comfortable, utterly indifferent cat sprawled across James’s lap.
For a second—just a second—his grin froze. And then—loud, delighted, unrestrained—he laughed.
“Oh, this is actually brilliant.” His eyes flicked between James, Regulus, and the cat, realization dawning like a sunrise made of pure mockery. “Did you steal his cat?”
James blinked. “What? No! It followed me.”
Somehow, that only made Sirius’s grin wider.
“You’re telling me,” he said, voice full of mock amazement, “that Regulus’s deeply judgmental, deeply antisocial beast chose you ?”
Regulus closed his eyes for half a second. He could feel the migraine forming.
This was going to be unbearable.
Sirius turned to Lupin and Pettigrew, gesturing wildly like he was making an important announcement. Lupin let out a long, slow breath, rubbing his temple.
“Oh, Merlin. Here we go. ”
“James, mate, you—you don’t get it.” He gestured wildly at the scene before him. “That thing barely tolerates anyone. Reg lets him roam around the house and I swear to Merlin, the cat only comes back to judge us.”
Regulus scowled. “ He does not. ”
Sirius ignored him. “And now he’s sitting on you ? Purring?” He cackled. “Oh, this is bloody fantastic. ”
James looked down at the cat, who was now stretching luxuriously, flicking its tail against his arm.
“Well,” James said smugly, “what can I say? Animals love me.”
Regulus scowled deeper. The cat—his cat, his ungrateful little beast—nuzzled against James’s robes.
James’s smirk deepened. “Jealous, Reg?”
Regulus saw red. Sirius, of course, just laughed harder. “Don’t call me that.”
Remus pinched the bridge of his nose. “I give it two minutes before a hex goes flying.”
Peter nodded solemnly. “One minute, if James keeps talking.”
Regulus reached for the cat.
It did not move. Instead, it gave him a slow, lazy blink, as if considering the request, before turning its head and nuzzling back into James’s robes, utterly uninterested in returning to its rightful owner.
Regulus stared.
James looked down at the cat, grinning. “See? He likes me.”
Regulus exhaled sharply through his nose. “No, he likes the food you bribed him with.”
James scratched the cat behind its ears, completely unconcerned. “Same thing, really.”
Regulus narrowed his eyes. “Give him back.”
James shrugged. “I’m not stopping him from leaving.”
Regulus attempted, once again, to take what was his. He scooped the cat into his arms, holding it firmly against his chest—only for the little traitor to start twisting and squirming almost immediately, front paws pressing against his robes as if trying to push away.
Regulus frowned. “What’s wrong with you?”
The cat stretched its neck, looking pointedly back at James.
James raised his eyebrows. “Mate, I think your cat just dumped you.”
Regulus felt something tighten in his chest.
James Potter had a habit of taking things that weren’t his.
Not in a way that anyone could call him a thief—not really. But somehow, without trying, he always ended up with things that should have belonged to someone else.
Regulus had seen it. James had taken Sirius’s loyalty the moment they met, without even trying. Before that, it had always been just them – Regulus and Sirius. Then Sirius went to Hogwarts, and suddenly James was there, slipping into his place like it was always meant for him.
And James hadn’t done it on purpose. That was the worst part. He had never needed to fight for Sirius’s attention. He had just existed, and that had been enough.
And now, apparently, he didn’t have to fight for the damn cat’s, either.
Regulus tightened his hold around the cat, securing it firmly in his arms this time, ignoring the annoyed flick of its tail.
“I’ve wasted enough time here.” His voice was cool, detached.
Sirius didn’t answer right away. Then he let out a slow, sharp breath. “Right. Back to your lot, then?”
Regulus lifted his chin. “Obviously.”
Sirius let out a quiet scoff, shaking his head as he slumped back into his seat. “Yeah. Figures.”
That should have been the end of it.
Regulus should have turned, left, and been done with it.
But then—
The cat squirmed in his grip again—then let out a small, pathetic sound of protest as it stretched toward James. Regulus’s fingers curled tighter around its fur, a sharp feeling coiling in his chest.
Potter, for once, wasn’t smirking. Not fully. There was still the ghost of it, lingering at the corner of his mouth—something half-formed, half-held back, like he was waiting for the right moment to let it tip over into a grin.
But he didn’t. He just watched. Not gloating. Not teasing. Just looking.
And for some reason, that was worse.
Regulus turned away sharply, ignoring the way his stomach twisted.
He stepped toward the door, ready to leave, ready to put this entire ridiculous moment behind him—
But, of course, James Potter just had to open his mouth one last time.
“Oi, Black—”
Regulus gritted his teeth. “What.”
James leaned back, arms resting lazily over the seat, expression all mock innocence.
“What’s his name?”
Regulus should have ignored him. Should have walked away. But Sirius didn’t give him the chance.
“Cosmo,” he answered before Regulus could stop him. “Very on brand, don’t you think? Our mother would be so proud.”
Regulus’s grip on the cat tightened. “Shut up, Sirius.”
James tilted his head, considering. Then, to Regulus’s absolute horror, he grinned.
“Cosmo, huh?” He shot the cat an approving look. “Yeah, that fits. Regal. Stubborn. Dramatic.” He glanced back up at Regulus, eyes dancing with that same insufferable amusement. “No wonder he likes me.”
Regulus exhaled sharply through his nose, grip tightening around the cat as it twisted again—reaching for James, stretching toward him like a traitorous little bastard.
And then—
James, ever the menace, shifted slightly forward, elbows on his knees, and spoke again. But this time—not to Regulus.
“You know, Cosmo,” James mused, his voice unbearably smug, “if you ever get tired of being stuck with this miserable git, you’re always welcome to visit.”
Regulus froze. Sirius let out an explosive bark of laughter. Peter choked on air. Even Remus, who had been stoic through this entire disaster, pinched the bridge of his nose like he was bracing for impact.
Regulus exhaled slowly.
Very slowly.
Very deliberately.
And then, without another word, he stepped out of the compartment and slammed the door shut behind him.
There was a beat of silence.
Then, muffled through the door—
“Oi, James, you absolute menace—”
James’s laughter rang through the corridor as Regulus stalked away, cat still squirming in his arms, still reaching for the boy Regulus most wanted to hex into oblivion.
He was going to regret not hexing him.
He knew it.