Mycroft:
I discover Sherlock's little moment of indiscretion quite accidently. You see, I am not due back at the manor for another three hours, but I managed to snag an early train (it's amazing how many things you can acquire just by having the gall to ask for them) and so here I am: standing in my bedroom doorway, staring. My baby brother has his fist in his lap and my sheets pressed to his nose, and he's groaning rhythmically with each thrust of his hips. Dear God. It's a testament to how lost in the moment he is that Sherlock, who notices everything, has yet to discover my unexpected interruption.
I move quickly. In less than a second, I've stepped into the room and clicked the door shut and locked behind me. This draws his attention and he sees me- he almost cries out, until I lift my finger to my lips and he falls back against the bed, his chest heaving and his eyes wide. He's so brazen, my brother, that he doesn't even have the decency to look ashamed of himself. Instead he sits up and hisses, "You're early."
"Obviously." I flick my gaze down to his trousers, which are still hanging open, and resist the urge to lick my lips or swallow. Instead I let my stare wander back up to Sherlock's face, to the delicate tinge of pink that blooms in each cheek and the haziness of his eyes. "Finish, quickly," I say without really expecting to; for good measure, I add: "Mummy will send for us soon, I imagine."
Sherlock isn't so beside himself that he can't see through this. He smiles, slow and sneaky, and drawls, "You want to watch." It's not a question, and so I don't dignify it with any form of acknowledgment. I just sink down on the bed beside him, unclasp my cuffs, and push up my sleeves.
My brother has never been what I would call shy, but he is prone to theatrics and so I watch his slow, seemingly wary strokes with limited patience. "Do the thing properly, please," I sigh, leaning back on my hands, "or else stop boring me and go to your own room." It pleases me immensely when he scowls at me and hastens his pale little fist, working quickly but with an air of defiance in the set of his jaw. I'm aware, distantly, of the way my own trousers are tightening, but I keep my hands (now twitching, but only slightly) on the bed behind me.
He's stopped showing off now and he's thrusting into it again, his bottom lip between his teeth and his breathing ragged. His eyes seem unfocused, pale and overcast. It's the most beautiful thing I've ever seen. I have the sudden urge to touch him but it passes quickly; Sherlock has never liked being touched, for one, and while the age gap between us feels insignificant at times, my two years at uni have made it nearly insurmountable. I am twenty; Sherlock is fourteen. I have had sex (with whores, of course, but the point remains) while I doubt Sherlock has even so much as held hands (though, admittedly, neither have I…but again, the point remains). There is an entire world between us now, and while my brother is a genius, clearly, and he's able to understand so much (and so quickly) his social naïveté will likely only be worsened by the consummation of an incestuous relationship. Even this, allowing him to gasp and groan before me as his seed runs over his still-working fist, feels like too much. I wonder if it will be the ruin of me, this little whim of mine. I wonder if it will be the ruin of him.
"Clean yourself up," I snap, more sharply than I intend. He looks up at me, his unruly curls falling into his eyes, and there's something almost wounded in his glare.
Rather indignantly, Sherlock waves his hand (still sticky with ejaculate) in the direction of my bulging zipper and quite crassly asks, "What about yours?"
"I'm not in the habit of showing off, Sherlock," I manage with calculated airiness. I would prefer he grasp it, my poor impertinent erection, and in fact can quite easily imagine the feel of his long fingers, but I don't say that. Instead I say: "I'll leave that to you, dear brother."
"Good," he mumbles, wiping his hand indelicately on my pillowcase. "And I'll leave the voyeurism to you." In an instant he's done up his trousers and stalked to the door. Turning back to me (those gray-green eyes so stormy, the haze of arousal already cleared away) he spits, "You don't have to warn me not to tell anyone; I'm not an idiot. And tell Mummy I'm not hungry. I don't care if it upsets her."
"It will," I say, because it needs to be said.
"Don't care," Sherlock huffs, and he's gone, the door hanging open and his heavy footfalls retreating at a run down the corridor.
My shoulders relax, and the breath I've been half-holding leaves me in a slow sigh. I drop my head back and close my eyes. In a moment I'll get up, close the door, and fall back into bed. I'll touch the damp spots on my pillowcase with one hand, and the now-painful evidence of my shameful lust with the other. It won't take long; just the shifting of the cloth around it is almost more than I can bear. Then I'll get up, wash my hands, clean my face (and neck, Mummy does fret over the skin behind my ears), and go down to dinner. I'll announce Sherlock's absence; Mummy will cry into her palms, the skin of her hands near-translucent over her protruding veins and bones. I'll eat too much. I won't think about Sherlock.
But for now, it's all I can do just to breathe.