Disclaimer: I don't own a thing.

A/N: This was originally an extra entry for the Anti-Christmas gift exchange, written to fill in for somebody who dropped out at the last moment. The gift was given to serpensortia. The prompt was, "What if Crowley/Adam was really on Hell's side?" Well, my first thought was, if Crowley was on Hell's side he would take advantage of his connection to Aziraphale. And this is what came out of that.

Warnings: Angst, violence, character death, evil!Crowley.

The Last Favour

Aziraphale stared down into his cup of tea and sighed. "I wonder what this is all about," he muttered. "This worries me. I can't remember when there'd last been this much demonic activity around."

"I don't know what it is," Crowley said with an apologetic tone. "If I did know, I would tell you. You know that, angel."

"Yes, I know." Aziraphale briefly covered Crowley's hand with his own before sighing again. "I fear I'll have to report this... immediately."

At this, Crowley frowned. "I thought you already sent Upstairs a message last week," he said, sounding confused.

"Yes, I did," Aziraphale replied. "However, I was told to let them know if it happened again. And not in a message this time, either -- I'll have to go there in person." He wiped a stay lock of hair from his face, but it fell back. "I know this is a weird thing to ask, but will you watch me while I'm gone? I wouldn't want any demons sneaking up on me while I'm in Heaven."

Crowley nodded, understanding. The connection Aziraphale was going to use would send his angelic self up to Heaven, while his corporation stayed on Earth. "You know I'll always watch over you, angel," he said softly.

Aziraphale smiled faintly. "I know." He took a sip of tea. "And I'm eternally grateful for that."

Once the tea was finished, Crowley watched quietly as Aziraphale took out the candles, making the necessary markings on the floor. Once it was ready, Aziraphale turned to him, looking a tad nervous. "I'll try to be quick," he said quietly.

The demon nodded in response. "Say, angel," Crowley said then thoughtfully, eyeing warily the column of light, "can they shut that thing from Up There? Like, without waiting to receive your message or something?"

"Oh, no," Aziraphale said, turning around to look at the light as well. "I opened it, and therefore only I can close it. It doesn't matter, anyway, because I've set it to disappear as soon as I step out of it."

He never saw it come. He had his back turned, after all. However, suddenly he felt a horrible pain on his shoulder, a pain he hadn't experienced for, oh, it must have been millennia now, but one he still remembered. A pair of fangs was sinking into his flesh, sharp and long and so very deadly if so intended, and the poison spreading from them soon flowed into every part of his body, hot and painful. He could barely manage a gasp as he collapsed on the floor when the attacker's grip on him released, his body suddenly not obeying him as horrifying numbness spread into every part of it.

He was lying on his stomach, unable to turn, but then the attacker turned him to lie on his back. Crowley looked at him and smirked, a tip of poison still hanging from the tip of one fang. He wasn't wearing his sunglasses, and the golden gaze fixed on him was rather unnerving.

"Can't have that, now can we," the demon said quietly, and something very much akin to satisfaction flickered in his eyes. "So sorry, angel, but that portal has to stay open for the, oh, countless demons that'll head here as soon as I can get a word Downstairs. Thank you, though, for providing us with direct access." He sighed in a way that was obviously very carefully intended to seem simply bored. "I'm in deep shit Downstairs, angel, more so than ever. With this I'll get my name out of the worst books, maybe even earn a promotion. And if I have to sacrifice you to do that, then so be it."

"But... I thought..." Aziraphale stammered, looking up at him with wide eyes. "I thought you cared..."

"That was my intention, to make you think that," Crowley replied with a smirk. "And I did, too, at one time. I still care about you hell of a lot more than about anybody else I know in this rotten world, Above, on Earth, or Below. But, in the end, I'm a demon. And when it comes down to it, every demon cares only about themselves, period."

The angel's face was very pale, the wideness of his eyes now partly due to fear, too, not just the shock of the discovery. "I -- I thought you loved me," he whispered, obviously with great difficulty, as if the words were stuck in the back of his throat.

Crowley clicked his tongue. "Love? What's that? Demons don't love, angel. We had it burned out of us in the Fall. When they make you a demon, nothing of the angel is left -- and that really means nothing. Angels are creatures of love. We are not."

A claw ran over the pale neck, and all Aziraphale's instincts were screaming at him, telling him to fight, to stop this all from happening. However, his body felt heavy and very uncooperative. He did attempt to raise his hand, but it fell down almost immediately, useless.

"Look, I can leave you here," Crowley said, "and soon this place'll be swarming with demons and you'll get killed for sure -- or captured, which you'll like even less. Or I can give you a quick end and you'll never know how it turned out. How'd that sound to you?"

Aziraphale shut his eyes briefly, unable to look any longer into those awful serpentine eyes that were so deceiving and enticing and beautiful. They'd held him captured for who knew how long. Years, maybe? Decades? Centuries, or even millennia? He could not honestly say when his strange infatuation had started -- and now they had finally become his downfall.

At last, however, he could no longer avoid looking into them one last time -- for he knew this was the last time, knew it from the way the poison was making him unable to move. Soon he wouldn't be able to open his eyes if he didn't do it now. In the hands of other demons, he wouldn't ever be, but his death would still be slow and excruciating.

Angels were designed as God's warriors, every one of them, creatures of fire and divine wrath just as much as they were those of light and love. Thus, even Aziraphale was a warrior. Bravery was one of the basic qualities of the angelic warriors, but what was bravery when you knew you were going to be dead soon anyway? And not just discorporation, no. This would be a permanent death. He wasn't entirely sure whether there would be anywhere for him to return to, had this been just a usual discorporation, either.

There was only one feeling that had anything to do with the situation. "Crowley," he whispered, his tongue and lips almost giving up on the task, "please... kiss me."

The demon didn't say a word, just watched him with serpentine eyes. Then he nodded as though he had just understood something important. Most probably he had. And, without a word, he leant down.

It was quick. A soft touch of lips on his own, and then, almost unnoticeable, two fangs sinking into his lower lip. Burning venom spreading out, unholy venom, even. And, suddenly, the numbness was washed away as darkness took its place and his consciousness left that plane of existence forever.

Once he was sure Aziraphale was dead -- which was about a second after the kiss; some of the poisons he had were quite impressive -- Crowley stood up, looking down at the angel. He looked almost... peaceful, lying there, pale and dead. He'd seen the angel like this several times before, of course -- but then, he had always known the angel would come back.

Still, he didn't find it in himself to regret his actions. He was a demon, after all.

With a thought he summoned unholy fire into his hand, lighting Aziraphale's clothes -- so incredibly old-fashioned and ridiculous, yet so very much like the angel. Making sure the fire didn't catch anything else -- it would all be destroyed soon enough, and he didn't want to attract the firemen if it wasn't absolutely necessary -- he watched as the angel's body was burned into ashes. The least thing he could do in return for the millennia of varying stages of companionship was to make sure no demon -- well, no other demon, anyway -- would get their claws on him. Crowley knew all too well what they would do to an angel, even a dead one. Especially a dead one, it sometimes seemed.

And besides, he didn't want anybody to know he had venom that could kill an angel in a second. He got enough snake comments as it was. Sure, he didn't really mind it, he was a serpent by nature after all, but after about ten thousand times it got quite old.

There was a very noticeable lack of a knock on the door before the first demon barged in. Crowley smirked. Oh, yes, it would work well enough. The demons would arrive, they would attack, and no matter what happened, his position could only be improved.

He licked a drop from his lips, smirking. The combined taste of one of his finest poisons and angelic blood filled his mouth.