Received this prompt on 2014-08-12. It went through two different plots before this one, and I'm still not sure I'm happy, but this prompt isn't working with me for some reason. I hope you all enjoy anyway~

Cross-posted from AO3 same date.

John was supposed to have had a heat with an alpha as soon as he got out of the army. Well, he was supposed to have one once every three years, but he was about a year out from his invalidation, and he'd yet to find one who'd willingly bed down with an omega as broken as he was. So he'd had to resort to desperate measures. He'd begged Mycroft to get Sherlock a case, and then started working himself from his suppressants. The second his alpha flatmate was out of the flat, John had made the call. Now he was staring down at a tense (young) alpha rentboy waiting on 221's stoop.

He hurriedly beckoned the boy inside, and there was a pause before he followed John, every step hesitant. His nostrils kept flaring as he took in the thick layer of alpha pheromones coating every surface within the flat, but he didn't ask where John's alpha was. The omega ignored the rentboy's unease and limped up the stairs to his bedroom, his leg muscles constricting with phantom pain.

The doctor was well aware that having the rentboy come to Sherlock's territory would put the young alpha into a more feral mindset, and he'd already glimpsed flecks of red in the boy's eyes, but John had already spent all his savings having a rentboy service him during his entire heat, and he couldn't afford taking the boy to a hotel for several days. More than that, Sherlock's scent never failed to comfort him, even if the alpha himself failed spectacularly in that department, and he'd be able to scrub the rentboy's scent from their home before his flatmate returned. He could leave it, it was well within his rights since they weren't even dating, but John wasn't sure what the alpha would do if he smelled another alpha in his territory.

John stripped in seconds, his heat boiling just under his skin, slick already coating the back of his thighs and drenching his pants and trousers. He turned to face the rentboy, about to ask him to lay on the bed when he was shoved from behind onto his mattress, bent over at the waist as he was filled suddenly and painfully, without preparation. He shouted at the burn and the stretch and tried to turn around, tried to face the young alpha who'd appeared young and docile only seconds before. But a hand clamped around the back of his neck, fingers pressing on his scent glands making him uncomfortably pliant.

"I don't want to see your face, omega," the rentboy growl. The rejection made something clench in John's chest and he went limp in the boy's hold, turning his face into his sheets. Apparently he couldn't even pay someone to pretend to like him or his body.

The sex hurt. The alpha's cock reached where it was supposed to, but it wasn't used kindly. Every thrust brought pain and made John's fingers curl in the sheets. He felt ashamed. Humiliated. He was a doctor, a military captain. He didn't tolerate this treatment from alphas in his life or in his bed. But he was desperate. He didn't need a mate, just someone to see him through his heats while he had them, and his inability to find a partner for the short bursts of time had reduced him to the pathetic state of needing to purchase a rentboy. Tears pricked at his eyes as the growing knot began to push against his already tender rim.

A loud growl from his doorway had the alpha pressing him to his mattress freezing mid-thrust. The both of them turned their heads, and John's heart stuttered in his chest at the sight of Sherlock standing just inside his room. Staring at them. Staring at John bent over his own bed like a whore, begging, if silently, to just be filled.

"Get out!" the omega shouted, voice cracking with his shame of being seen like this. He scrambled for something to drag across his body, hide the point of penetration from the alpha's all-seeing eyes, but the hand on the back of his neck tightened. Unwanted arousal from scent gland stimulation made him cry out and convulse around the alpha inside of him, and Sherlock's eyes narrowed.

"The omega is mine," the rentboy growled, his thrusts renewing at a rougher pace as the pressure forcing John's face to the bed increased.

To John's, and his heart's, surprise, Sherlock stalked forward, his presence in the room seeming to grow as he approached, his dark coat making him loom.

"You will get out of him or I will rip you out of him," the older alpha growled. The rentboy's hips stuttered and then Sherlock struck.

True to his word, the younger alpha was ripped out of John, and the omega cried out at the loss, his hole fluttering around empty air. The heat under his skin rose again, flames licking at his insides as he crawled fully onto his bed, curling around his cramping belly as he watched Sherlock clamp a hand around the back of the rentboy's neck and manhandle him out the door.

"I haven't gotten paid!" the young alpha cried, voice echoing in the stairway. John couldn't make out Sherlock's reply, either because the volume was too low or because they were too far away, but he could hear the rentboy yelp shortly before the front door slammed shut. Alone in his room, John began to tremble and sob as he rolled onto his belly and pressed his fingers to his aching hole. Now he would have to weather his heat unaided by even a toy, something he hadn't anticipated needing and so hadn't purchased.

Without warning, John was being shifted, turned and tugged, back to the way he'd been positioned with the rentboy. Before he could turn, find out who or why, a cock was pressing into him, thick and slow, and the omega keened at finally being filled again. Confused as to who was mounting him, he twisted his head over his shoulder and found Sherlock behind him, fully dressed, beautiful grey eyes gone alpha red.

"Sherlock!" he gasped, surprised beyond measure. "What-!" The alpha ducked down and pressed his lips to John's ear, cutting off the rest of his question.

"I am going to knot and mark you right here and right now so that I never have to see another alpha touching you again," Sherlock growled, not bothering to wait for an answer before he curled his hand around the front of John's throat, his hips sharp and fast as his cock pierced the omega again and again.

The doctor, for his part, could only keep a tight grip on the sheets and hold on for dear life as he was filled over and over, the heat kept just barely at bay by the thick length inside of him. There was a slow rumble just above his head; Sherlock hadn't stopped growling. The hand around his throat tightened, pulling his arse harder and faster into his flatmate's pelvis. There was a new knot pressing against him now, stretching him a little bit more with each thrust.

His orgasm, non-existent under the first alpha's administrations and building high and tight under the second's, punched through him as the knot popped past his rim. He was yanked up against a still-clothed chest as teeth punctured his skin and his scent gland, bonding him to his flatmate.

It wasn't until his cock had stopped pulsing and the first of the alpha's orgasms had passed that John realised he was still standing, held tight to Sherlock's chest and teeth still embedded in his neck.

"Sherlock?" he said, voice cracking.

The teeth in his neck pulled out and he whimpered at the feeling, his skin throbbing with the new mating mark.

"If you invite another alpha to our nest again, I will rend them pelvis to neck and mount you over their corpse." The threat and the possessiveness in the words sent a shiver down John's spine.

"You said you weren't interested," he rasped in reply, shifting on his new mate's knot. He didn't say that it felt like Sherlock just hadn't been interested in him, which had long been a mark against his already low self esteem.

The hand around his neck tightened and an arm like a bar wrapped around his waist, worming just a little more of the thick alpha cock into him, the knot pressing on his prostate so intently that he started trembling anew.

"You were mine the moment you stepped into Bart's, John Watson," Sherlock growled. "And you'll be mine until death."

The alpha came in him again, and John had neither the strength nor the will to deny him. Not that he could. Sherlock was right- John had been his since Bart's and would be his till death.

FIN

Thank you for reading! Please let me know what you thought, good or bad, in the Comments, and if bad, please be constructive so that I may better my writing! :3 Also, if you liked the story enough to want to promote/rec it on tumblr, instead of creating a new post, please reblog either the original prompt fill (themadkatter13fanfiction tumblr, post/106745518963) or the typical story info post (themadkatter13fanfiction tumblr, post/106745526908)! Thank you so much! You are, of course, also more than welcome to follow me on tumblr as well! :3 Tschüß~