Fire requires fuel, oxygen and energy. Flames are the result of an exothermic chemical reaction. The heat of the flames will keep the fuel at ignition temperature for as long as the chemical reaction continues.
None of these things are true for hellfire.
Hellfire requires lost faith to burn. Its flames are the result of hope being subsumed. The heat of the flames will turn anything hopeless to ashes for as long as sorrow remains.
The fire ravaging AZ Fell & Co wasn't hellfire when Crowley arrived. It was hellfire by the time he left.
It burned away authorial dreams. Crowley felt the flames crackling through a page at a time, scorching along the edges of what might have been. The smoke would've choked a human; Crowley, if he was honest, didn't find it particularly pleasant either. It stung against the back of his throat and curled nausea around his stomach, sticking to the holes in his corporation like treacle.
Surrounded by light and heat with no angel in sight, he screamed and cried and watched as the bookshelves cracked and darkened, the books turning into dust as the flames licked up one shelf at a time. Somewhere in the shop, he realised slowly, might be Aziraphale's body, but war had shown him enough charred flesh and empty eyes that the idea of looking for it seemed distasteful at best.
(There was no Aziraphale in the fire. No blackened bones. No mote of ash. No hope or love. There was nothing. Inside a safe in a very expensive Mayfair flat, though – there had been something. Enough hope to drown a demon, held in a tartan thermos. It was gone.)
Stepping into hellfire while wearing Aziraphale's face was a comparative walk in the park.
“You should get a fire alarm,” said Crowley. “Surprised Adam didn't put one in.”
He'd put in a children's section, fixed the shelves, restored the books and added a bowl of sweets, but hadn't thought to protect everything he'd created.
“Oh, really, Crowley,” Aziraphale tutted as if he'd just suggested installing a stripper pole in the middle of the shop, “a fire alarm?”
“Right. Yeah. Stupid, thinking an uninsured shop full of occult paper where you sometimes leave candles unattended might benefit from a fire alarm. Not like it burnt down a few months ago.”
“I hardly ever leave candles unattended these days,” protested Aziraphale, “you can't blame me for some silly man intruding and knocking those ones over.”
“Yeah. Like I said, stupid.”
Crowley rolled over on the sofa. The shop didn't smell of smoke any more (or at least, no more than any other shop in London, haunted as the city was by fires both large and small). Aziraphale hadn't even been there when it happened. The only blaze remaining was the one scorched behind his eyelids, and that one was just electricity misfiring, trying to convince him of a danger long past.
“Crowley. Are you – worried for me?”
How was he supposed to answer that? There was nothing he could admit to which wouldn't be hideously embarrassing.
“Fine. You've caught me. Thought it'd be funny to make the neighbourhood listen to a fire alarm at three in the morning. Fiendish.”
Aziraphale didn't reply. He instead strode over to his desk and started to rummage. Adam had made an attempt at restoring its clutter, but it was the sort of low-level, term-time clutter that a schoolboy might leave on a bedroom surface rather than the angelic and esoteric clutter of centuries. He found what he was looking for much more quickly than either of them expected.
Crowley rolled over when he heard the rattle.
Aziraphale had the little box – a box, not a book; something he'd bought, not something he'd picked up – clutched tightly in his palm.
“These ones are called safety matches,” he said, light and conversational, when he joined Crowley on the sofa. “Ingenious, really. Do you remember that nasty business with the match girls, and how their poor faces would start to rot? These ones don't do that.”
“That's not,” Crowley croaked. He coughed in a vain attempt to stop himself sounding quite so unhinged. “That's not why they're safety matches, angel. It's because the old Lucifer matches used to burn up in your pocket sometimes, remember?”
“Oh? Well, that match factory is a block of flats now, anyway.”
Aziraphale pushed the box open and slid one of the pale matches out. It was short and looked ridiculously delicate in between his fingers. It wouldn't burn for more than a few moments, Crowley thought, before it started to singe him.
“You know fire is just energy, don't you?” Aziraphale continued.
“This coming from an angel who thought dolphins were a type of fish,” Crowley muttered, “now he's trying to teach me physics.”
Aziraphale looked unimpressed.
“Crowley, what do you think is going to happen if I set this place on fire?”
Crowley shrugged. “Dunno.”
Aziraphale's fingers tightened on the match. He rested it against the box while he kept on talking.
“Perhaps I misspoke. What do you think can possibly happen to an ethereal being who kept a bookshop perfectly safe for decades before electric lighting came along?”
Aziraphale scratched the match along the outside of the box. Crowley stopped breathing for as long as it took to light.
“Your books,” he finally said, “they'd burn up. You love them.”
At that, Aziraphale had the gall to look amused. “Poor dear fiend. I do love my books, it's true.”
The flame licked down the match, crackling as it went. The head continued to glow red while the blue base of the burn travelled downwards until it finally reached Aziraphale's fingers. Where a human might wince, Aziraphale did nothing of the sort. A curl of smoke rose as the heat reached his fingers, then – stopped, leaving his flesh unsullied.
“Are you OK?”
Aziraphale smiled again. “Perfectly fine. Only a little energy. I told you that before.”
Crowley dreamt of the fire again that night. The books burned and the shelves cracked and in the middle of them was an angel, wreathed in holy flames. Only energy, he smiled in Enochian before Crowley woke up, panting and sweating, nothing to worry about, my darling, my dearest fiend.
The following month was unseasonably cold. Even Aziraphale, who was usually only aware of the temperature thanks to the shipping forecast, wore a scarf around the shop.
Crowley was miserable.
“Angel, put the bloody heating on,” he tried, huffing into his hands as if that would help.
Aziraphale sighed. “I don't actually have any.”
“Bullshit,” Crowley said, more loudly than he'd meant, “there's no way it's usually this cold in here.”
“What I have,” Aziraphale continued calmly, “is a fireplace. But considering your last reaction to the idea of anything burning here, I wouldn't want to light it with you about.”
Crowley paused. The things in his psyche which had been uncoiling for the past month felt like it belonged in the dark. It wasn't ready to be exposed.
“If it was you lighting it,” he started slowly, “I reckon it'd be alright. We could keep an eye on it.”
I could keep an eye on you, he didn't continue, building and controlling it, letting it destroy what you wanted, feeding it – those were things that didn't feel ready just yet.
“Well,” Aziraphale said, smoothing down his waistcoat with a warm smile, “I do have a bucket of sand handy in case anything goes wrong.”
The shop was more pleasant after that.
Sometimes Crowley would watch Aziraphale build up the pyre, stacking logs neatly and stuffing them with old newspaper in a configuration that looked like something he'd learnt from a Boy Scout. Sometimes Crowley would do it himself, chucking too much paper and too many firelights on the pyre, then getting grumpy when the initial roaring flare died down into dark pulsing.
Sometimes when he napped the fire would spread and Aziraphale would open up his wings and say be not afraid and darling fiend and all energy is sacred.
Sometimes he was uncomfortably damp when he woke.
“I see they're building a new library,” Aziraphale said. Libraries had the privilege of being possibly the only new thing he'd be joyful about. “Oh, and it's going to replace that decrepit little one you were complaining about just last week.”
“Angel,” said Crowley, “please, I'm begging you, don't make me take you to another book sale. We can just,” he waved his hand, “the books here if you want.”
“Oh, no, they've already sold off any precious ones in their collection. And the popular ones still in good condition will be taken to the new place. No, the only ones left will be completely unsalvageable.”
“So this isn't another Alexandria situation for you, then.”
Aziraphale laughed. “Far from it. Although I suppose since the library there had largely declined before the fire, and was almost empty by the time it came about, a similar situation could be...”
“Could be?” Crowley prompted. (He didn't need to breathe. He wasn't going to breathe.)
“Could be engineered,” Aziraphale continued, more quietly than before, “without any great loss. Should Hellish forces decide to burn it down.”
“Wouldn't be worth using hellfire on some piddling little library,” said Crowley carefully. “The forces of Hell would just have to take a book of matches, maybe some lighter fluid.”
“Oh, of course,” Aziraphale agreed, “and fortunately it would be jolly easy for me to stop that sort of fire if I wanted.”
“You'd go to check it out, see if there was anyone in need of help.”
“Certainly. I'd have a walk around, perhaps. Make sure none of the infrastructure was damaged.”
“And you could,” Crowley swallowed, “you could escape. If you needed to. You'd be safe.”
“I have always found,” Aziraphale replied, “that in situations where I wouldn't otherwise be, a dear friend makes it so.”
Someone left the library unlocked that evening, which was unusual as nobody had been inside for several weeks at that point.
Aziraphale was right – none of the books here were worth anything anymore. The children's books were missing key pages, or they were scribbled on so hard that the words were unreadable. The adult books were falling apart, mass market paperbacks that had been read so often they were torn, water damaged or smudged.
The library as a whole had seen better days, although luckily (miraculously, the council would say later) contained no asbestos, no polystyrene and no lead.
Crowley picked a book up from the shelf. It had once been a science textbook and contained some incredibly inaccurate facts on gender and psychology, so he felt maliciously fine with ripping out the pages and stuffing them in the empty spaces where better books have once been.
“Is somebody there?”
Crowley was tempted to yell back that no, there wasn't. Instead he gathered armfuls of books to carry to Aziraphale, who was standing between 212 and 234.
“You shouldn't be here,” he said, letting the books fall at the angel's feet.
Crowley saw Aziraphale's eyes lower briefly, a flicker of unease and hunger and despair all rolled up in an oddly erotic package. Berlin and the end of Institut für Sexualwissenschaft had left their marks in more ways than one.
“Are you going to burn these books, fiend?”
“I don't have to,” Crowley said quickly. “I could get some other ones, or we could just call the whole thing off.”
“Well, goodness, since you're going to burn them anyway, I should stay and protect what I can.”
“Right. Yes. Sure.”
Crowley pulled the matches out of his front pocket where they'd been pressing into his thigh. He knelt down in front of Aziraphale with his hands shaking and ran his fingers over the remains of the books before reaching it up the soft corduroy of Aziraphale's trousers. He was meant to be a fiendish arsonist, reaching for fire and destruction, not a fallen angel waiting to be petted.
Aziraphale's hand in his hair made it easier to light the match.
Just energy, Aziraphale said. The tiny slip of burning wood between his fingers was just transferring energy.
The paper caught easily.
Crowley watched the line of light snake up the edge of the paper. His glasses hung from the front of his shirt; if it got too bright, he'd use them, but for now he was content to watch the pages catching, their dead stories made bright and warm.
“Fiend,” Aziraphale breathed, and pulled his hand back.
The fire lit him from below, casting flickering shadows across and behind him. Crowley stumbled back to watch the flames deliberate – the books had all caught, the blaze starting to spread to the bookcases, smelling of clean ash and rising smoke.
The roar and crackle reached to the shelves, devouring the card and paper with no regard for the angel amongst them. The flames were almost invisible in parts, but the trail they left was obvious.
There was no bucket of sand here. No tap for water. There was only fire, crawling up the shelves and devouring everything it could reach.
The paint on the walls had been blue, maybe, once upon a time. It crackled and bubbled as the flames grew hotter, reaching towards the ceiling for new material to warp and own. The metal nails that had once hung posters turned red, then white, then started to distort in shape.
“Aziraphale,” said Crowley.
Turning from staring into the brightest part of the flame to staring at the angel in the middle of it meant Crowley needed to give his eyes a little time to adjust – but there was Aziraphale, standing as happily as if somebody had suddenly decided against buying a first edition.
“Yes, dear?” Aziraphale asked, as calmly as if he was discussing the cricket score.
“Dear heart,” said Aziraphale.
He shrugged his shoulders. He rolled his head. He stretched – and his wings stretched out with him, and suddenly every flame was dull and meagre in comparison.
“You're safe,” Crowley repeated. His face was wet. If not for the fact the sound was drowned out by the roar and crackle of twisting wood, he would have been able to hear his tears evaporate with a hiss as soon as they hit the ground.
“We both are,” Aziraphale said. “We always shall be.”
He pulled his wings around the two of them, and the sounds of the fire died down. There was only brightness – ineffable brightness – gleaming with energy and hope.