This is an interesting turn of events for me.

Moriarty.

And Mycroft. Ohyes.
Hints of Sherlock and a dangerous obsession.

Another masturbation fic?

Yes. It seems that I have a thing for Moriarty with himself.

Mycroft knows that Moriarty can see him.

It’s never stopped either of them.

His brother’s name is scratched into the wall, across the mirror, dug deep into the metal and glass of Moriarty’s cell. Mycroft has deduced that he uses the metal chair to scratch the words- they had him stripped and searched before bolting the door shut- it’s the only possible explanation he’s been able to come up with. He’d ask Sherlock, but… his brother doesn’t and won’t know that Moriarty is held here.

Sometimes James Moriarty will scream Sherlock’s name until his voice is hoarse and broken. Mycroft will watch and listen and wait it out, he will try to figure out where this dangerous obsession stems from and how it will affect his brother when they are forced to release Moriarty back into the world.

And sometimes, like tonight, Moriarty will lean back in that cold metal chair with his knees spread apart. He’ll look at the two-way glass and know exactly where Mycroft is standing, his eyes will darken and his lips will tug into a small and twisted smile. His right hand will move to his knee, his fingers will dig into his kneecap, he’ll drag his hand upwards and it will leave imprints of his nails into his pants- all the way up his thigh. His hand will slip under the waistband of his pants and he’ll sigh- his tongue will dip out and slide across his bottom lip and he’ll leave his mouth parted.

And Mycroft will watch. Just like he’s been watching for several nights now. Morbid curiosity is how his mind explains it away; his body hasn’t come up with suitable excuse yet.

His other hand will clench into a fist at his side, or, sometimes he’ll bring his hand to his lips and press his index and middle fingers into his mouth- slow- he’ll drag his tongue along the underside or spread his fingers and curl the tip of his tongue through them obscenely. The outline of his fist, wrapped around his cock, will show through his pants and he’ll groan. Most of the time it’s just a low humming sound- but sometimes, sometimes- it’s a breathy Sherlock.

He’ll let his eyes fall closed if he’s whispered Sherlock’s name- reverent like he’s praying for salvation.

But sometimes, like tonight, he’ll look through the glass and know where Mycroft’s eyes are. He’ll lean forward on his chair and look up at the older Holmes from under dark eyelashes. His wrist will jerk, his hand will slide faster up and down his cock. He’ll tilt his head to the side and lick his lips, his hips will rise off the chair, his breath will come out in quick, sharp gasps. A sheen of sweat will spread across his body and bead at his temples and along his forehead. He’ll moan, loud and dramatic and pump faster still- Oh.Oh.Oh.

He’ll keep his eyes locked onto Mycroft’s, the corner of his mouth will tilt into a mocking grin.

And then Moriarty will come with a rise of his hips and nothing more than that smile.

It makes Mycroft believe in the Devil.
And worry about his brother.