A/N: I have no idea where this idea crawled out from... but here it is, my loves!
Isabelle Lightwood frowned, attempting to bury herself in a volume about demonic cults and rituals, and names of demons (most of which had three). And she was trying in earnest, as the information was valid, was part of her training... But truly, she speculated, who, aside from her brother actually read that stuff? Other than... well, that was easy! I'll just get Alec to summarize it for me! Knowing him, he's got the stupid book memorized.
"Jace," she grabbed the attention of her also-bored-out-of-his-mind blond companion. "Can you go get Alec? I have a... question for him."
"A question so mind-blowing it's keeping you sitting in that chair, unable to get him yourself, I see," retorted the blond. "Because I, as a matter of fact, happen to be attempting to go forth and multiply my already vast knowledge." As was his seeming custom whilst speaking, his fact smoothed into a self-assured grin and his eyes took on a holier-than-thou air.
Isabelle merely rolled her eyes, unwilling to allow her simple question suddenly make her the dunce, as she'd seen Jace do many, many times successfully over the years (usually, but not limited to, Alec or to herself). "Just go get him, okay?"
"First, Isabelle, what is the situation that calls for our dear Alexander? And secondly, why should I concern myself with your question?" He raised an eyebrow worthy of envy via his significant other.
"Do you want to keep reading this crap or not?" Her tone was clipped and simple. Too much argument with Jace would get him talking and once he was talking, she'd be here the entire night, rather than a much more desirable date with a certain vampire. "The idea is; You get Alec, he tells us because he's a sucker, we don't have to suffer through this, you can go shag Clary, and I'll be off and on my way for now."
"I'm all for shagging Clary," Jace allowed, earning a shudder from Isabelle, "And since your large backside will move not from that chair, evidently, I suppose it's left to me to save Clary from a night of boredom!" And that, was that and he was off before Isabelle could lop his head off for the commentary on her backside.
Jace boredly ascended the stairs, looking about himself. About two-thirds of the way up the flight leading to Alec's bedroom, he began to hear peculiar noises. They were muffled, but definitely volumous, he could tell. And there was likely some sort of... agony? Physical stress? Some sort of trauma coming from the upstairs bedrooms. Obviously, this being an Institute, no demon was savagely devouring his Parabatai (the only other male possibly present), yet Jace found himself slightly concerned and exceedingly confused.
The sounds grew in volume as he continued his trek, and also varied slightly. Yes, there was an occasional scream-like noise, but also sharp gasps, and some sort of slow, drawn-out groan. Even, Jace noted, an unintelligible, hoarse word or two was heard, though he couldn't make it out. Also, as he walked on, he realized the noises could only be coming from the bedroom belonging to his soul-brother. And while it was something frightening he heard, their soul link gave Jace no indication that his parabatai was in any danger.
What, in the Angel's name, is going on in here? He thought to himself. Jace approached the door, and confirmed that the sounds came from behind it. From this close, it was almost as if two voices were making the noise. Before he allowed himself to think upon it, which likely would have bettered his outcome, the blond shadowhunter knocked, yet threw open the door anyway.
"MMM," the shadowhunter bit his lip, ignoring the far louder groan of pleasure his body involuntarily surrendered him to. "Magnus..." He whispered through heavy breaths and soft sounds escaping his throat. The warlock was deft, he was strong... Alec gripped at the bedsheets, half maddened as he was loved deeply, wholly by the warlock behind him who simultaneously caressed his arousal at the front.
Alec neared the wave that would burst forth from him, his heartbeat as intense as the pace given by his lover, his whole body could feel it.
Yet he was ripped horribly from the pleasure, the world in which there was only he, Magnus and the cotton sheets, from intense and fiery touches by a blinding light and blond hair.
"Alec Isabelle... needs.. you..." Jace began, eyes widened for a moment, clearly taken off his guard and expectation. Alec? Intercourse? The two did not add up in the mind of Jace Herondale.
Horrified, the dark-haired one flung a blanket over his exposed front, face reddened and his heart hammering as though he were being chased like a demon. "Jace!" He hissed. "By the Angel, Jace, get out! I'm … indecent!"
Magnus, on the other hand had a visage that only expressed annoyance at his being interrupted, and his having to halt his endeavors with the tasty little shadowhunter who lay in from of him. He stretched himself out, rejecting any self-consciousness, and looked to the blond shadowhunter. "As am I." He glared.
"... Isabelle doesn't need you that much." Jace shook his head, leaving the room promptly, only turning slightly at the loud request of "Shut the door!" From Alec.
Next time, Isabelle can fetch her own damned brother.