Remus Lupin is back to being mild-mannered, much to James and Sirius's disappointment.
The two boys hadn't paid Remus much attention before, only enough to notice that he seems exceedingly dull, prone to boring habits like reading by the fire, helping first-years with their homework, answering questions when professors asked them, and sitting up-right and proper while sipping tea at breakfast. All this boring instantly reappears when they see Remus the next day at school, and goes on long enough at that James proclaims his official disinterest in the Remus mystery and decides to move forward with his other schemes.
Thank Merlin, Remus thinks when he hears the proclamation. He was starting to get antsy with Black and Potter watching his every move, especially with the full moon coming in couple weeks. He didn't need or want the attention of two mischievous boys.
The Black-Potter duo are difficult to completely avoid though, as Remus finds out the next week.
Remus is sitting on the floor minding his own business, peacefully reading in an aisle between the bookshelves in the library, when he hears some kind of explosion and then a hoot of delight and the wild, maniacal laugher that could only belong to Sirius Black. An all-encompassing creaking noise has enveloped the room and there's a sound awfully similar to a hundred-thousand books falling off shelves, accompanied by ridiculously huge crashes that can only mean that the beautiful, elegant, antique, bookcases of the library are falling into each other like dominoes.
He has only a moment to be stunned before the charms books around him are falling onto the floor, some of which are shrieking their own displeasure at this turn of events.
"BLACK!" he shrieks murderously, pulling himself off the floor at the sight of the perpetrator racing past. The boy whirls around at the sound of his name, eyes wide when he spots Remus between the shelves.
The bookcase beside Remus is swaying ominously just from the reverberations of the other shelves and he leaps up to steady it, with some success, when another bookcase rams into it and all hope is lost. Waterfalls of books fall onto his head as the shelf tips over. One book of which manages to hit him with its corner just so, causing his vision to black out and bringing him to his knees. This turns out to be a good thing. Remus is very fortunate that he seems to be in the exact middle of the domino bookcases, which had apparently been set off from both sides, resulting in a protective tower that is the only reason he isn't crushed.
Remus is, understandably, momentarily dazed.
"Lupin! Shit!" says idiot Potter's voice.
"I don't know how this happened, we cast a wizard detection spell on this whole section of the library before we—" panics idiot Black.
"Come on Lupin—you know we wouldn't kill you on purpose!"
And they know they are in deep shit because this is Lupin and these are books and its pretty obvious that Lupin considers books to be holier than life, sex, and the Dalai Lama.
Remus can feel a murderous kind of rage building up in him, rage that overshadows the slitting headache and deep muscles bruises he expects from the shower of book he just received.
They are startled when Remus growls—actually growls—and swiftly gets up to wrench them by the cuffs of the robes, out of the library, ignoring their protests and dumping them unceremoniously outside the door. He leans in to whisper, feeling the effect will be stronger than him shouting, "Don't ever let me see your idiot faces in this library again." And he's pleased by the looks of sheer terror they give him, deciding that this horrible event may have the unforeseen benefit of Potter and Black actually leaving him alone.