Disclaimer: I don't own Harry Potter or any of its contents, and I'm not making any money off this.

A/N: This isn't properly British.

Regulus finds out from overhearing a talk between Potter and Sirius, who never was very good at keeping secrets. Regulus knows that Sirius holds this one very dear to his heart though, because Regulus imagines it must take a lot of strength to know something so large and never tell a soul.

Regulus doesn't tell anyone he knows. At first, he thinks maybe he should. It's a safety issue, isn't? To have one of those on the loose... but then he thinks they've made it so many years without incident that they must know what they're doing—there must be something making it okay. Then he thinks it isn't his secret to tell, and besides, Remus Lupin is so utterly sweet and adorable that Regulus just can't bring himself to destroy Lupin like a reveal would.

Regulus doesn't spend much time with his brother's friends, of course. Sirius clearly hates him, for reasons he completely doesn't understand, because Sirius is the one that changed, not him. Blacks are supposed to be in Slytherin, and Regulus really only does what's expected of him. Sirius does whatever he likes and runs around with Potter and Pettigrew and Lupin pulling off childish pranks and generally underachieving. Right now they're in the library 'studying' one table away from Regulus, except he's pretty sure from the snippets of conversation he catches that Potter and Sirius, at least, aren't at all researching anything academic.

"What if we put a self-extinguishing spell?" Sirius suggest quietly, so that Regulus has to really perk his ears up to listen. "Maybe we can set them to stop when they hit head-level or something..."

"And if they don't work and you take someone's eye out?" Lupin asks evenly. Sirius just shrugs—somehow Lupin gets away with scolding him where no one else does.

But Regulus does understand. Lupin has such a good way of scolding—he's sweet about it, and his voice is never accusatory or degrading. He shifts in his seat and raises the tip of his quill to his lips—Regulus thinks it might a sugar one from Honeydukes. Lupin's at the end of the table, across from Potter and Sirius—right next to Regulus one table over. Sirius' group of friends never look over; it's as if Regulus and his fellow Slytherins are invisible.

The Slytherins are much quieter. They're all bent over their books, as intent on studying as Lupin looks. Regulus is looking down like the rest of them, but mostly observing what goes on out the corner of his eye.

"Maybe if we can find a way to control the direction they fly in," Potter suggests. Lupin nods without looking up, his soft, chestnut hair bouncing attractively atop his head. He starts to nibble his lips around the quill—they're glistening slightly with drops of sugar. Regulus can't help but zone out, wondering vaguely what they feel like. What they taste like. He bets Lupin tastes sweet—bet he feels warm and gentle. Does the secret effect him normally, or in the bedroom, Regulus wonders? He looks so innocent and fragile, and he's always in and out of the hospital wing—before Regulus would've thought it so easy to dominate him—to bend him over a table and ravish his pretty brains out... but is there more than that, perhaps? Maybe he isn't so demure as he looks—maybe the beast inside him comes out when he's in bed—maybe he's feral and wicked. He probably has more stamina and can probably take more, take it harder... does he give it harder, too? If Regulus tried to trap Lupin in a deserted corridor, would he find himself losing the fight? Does Lupin make love like a human, stretched out luxuriously, or does he fuck like an animal, mounting his mate and thrusting wildly? Does he bite? He probably uses lots of tongue—the way it darts out, small and pink, around the tip of his quill is almost more erotic than Regulus can stand. He finds himself shifting awkwardly in his seat, wondering if he should take off his robes and drape them over his lap.

Regulus seems to have missed a few things during his daydreams. Potter and Sirius are now packing up, and Pettigrew looks desperately like he wants to follow. But Lupin purrs around his quill, "That's alright; I think I'll stay and finish this essay."

Potter chuckles, "Always the hard worker, Moony."

The nickname now makes sense. Potter reaches out and ruffles Lupin's hair—Regulus has a flare of inordinate jealousy.

"Well, you'll need something to copy from later," Lupin laughs. He blows a fake kiss as his friends leave, lips puckered and perfect.

Regulus doesn't know what comes over him. As soon as the others leave the library, he stands up, walks abruptly around his table, and sits down across from Lupin.

Lupin looks up and smiles.