A/N: Been wondering since the first time I saw Good Omens where Crowley got his Astronomy book from, so I wrote this.

The Extremely Big Book of Astronomy

A Good Omens fanfiction

Crowley stepped into the bookshop, not bothering to halt for – or even glance at – the closed sign. In Crowley's world, closed signs were something that happened to other people. Besides, Aziraphale wouldn't mind – it wasn't as if he were a customer. The angel knew how rare it was for Crowley to even pick up a book in passing, perfectly aware of just how few books graced the inside of the demon's flat (he did not, as he'd told his hellish associate rather haughtily once before in an uncharacteristically heated moment, count gardening catalogues or vintage T.V. Guides from America, thank you).

In all fairness, however, it was also somewhat rare for Crowley to come into the shop twice in one week, let alone the very next morning after he'd been visiting only the night before for a social drinking binge in the back room.

They had to be careful.

It wouldn't do, Aziraphale liked pointing out, giving Heaven and Hell anything worth taking note of.

Which was why the angel had only been in Crowley's flat once. He had seemed anxious, wringing his hands and looking about with darting eyes the entire time.

"I don't think," he'd said, very softly, with a flushed and apologetic expression camping on his face, "my side would like my being here."

Crowley tried to tell him that Heaven probably didn't care where he was – that they had more important things to do than worry about where one earth-bound Principality spent his afternoon.

But it made no difference. He simply wouldn't settle, couldn't relax.

The best Crowley could do was distract Aziraphale with a brief tour of the where he kept the plants, whose distress the impressed Angel was entirely oblivious to, remarking only that they were beautiful and very well cared for indeed.

"My plants always get those ugly brown spots," he remarked. "Then they shed leaves all over the books. That's why I had to toss them out ages ago."

And no doubt, Crowley knew with satisfaction, several of the plants began having post traumatic flashbacks at the mere mention of a brown spot and (shudder) shedding. What if such a tragedy should befall one of them, after all? Their owner wouldn't stand for it; he would be merciless.

Anyway, the visit to Crowley's flat had put Aziraphale so far on edge that the next time they met, it was at the British Museum, and Crowley had to make rather an annoyingly elaborate pretence of talking to the world's most boring curator and acting like he was there for some exhibit or other before Aziraphale – who'd been observing the demon from the corner of his eye and shaking his head, almost imperceptibly, every time he took a step nearer to him – was finally convinced no one was watching them. Only then, with a little sigh of relief, had he waved and said – quite cheerily, despite Crowley's by then severely dampened mood – good afternoon.

The bells above the door jingled loudly and Crowley was mildly surprised when the angel didn't call out, "Back here," or "I'm at my desk, dear," or "Closed! We're closed," if for whatever reason he didn't realise who it was despite them having made plans yesterday.

He shut the door behind himself. "Angel?"

"All right. Yes, naturally I'll come and fill out the report today. I don't suppose there's any chance of recovering the pilfered item? No?" This was not addressed to Crowley who, a moment later, heard the click of an old phone receiver being put down.

Then a sniffle. Aziraphale's voice had sounded as if he were on the verge of tears.

"What's the matter?"

Aziraphale jumped, springing up from the chair in front of his desk – which was flung backwards rather impressively in his panic – to his feet. "Oh." He smiled shakily. "It's you, Crowley. Hello."

"Who was that?"

"The police." He closed his eyes and inhaled deeply. "I've just had to phone them. It's quite terrible. There's been a robbery."

Opening his eyes again, the angel looked so pained that Crowley was strongly considering finding the robber himself and forcing the bastard to swallow his own tongue. That was one of Hastur's favourite punishments, and usually Crowley disapproved of it, but all rules were made to have exceptions.

"It was so unexpected," Aziraphale pressed on, face ashen. "I've never been successfully shoplifted from before. I suppose you'll give me a lift to the station to fill out a report?"

"Yeah, of course. What did they take?" Crowley wanted to know. "Not the Unrighteous Bible?" He knew how much Aziraphale treasured his rare Bible collection. "Did they get into the register?" The thing was such an antique, he didn't expect anyone would work out how, but you never knew, not for sure.

The angel shook his head. "No, no. The Bibles are all where they should be, and I'm not missing any money."

Crowley frowned. Now that he thought on it the place was rather neat for having just been robbed. No signs of a break in; no shattered glass or broken locks...

"You took the time to clean up after the thief left?"

"No. There was no mess. None at all. They were very quick and very quiet. I never actually saw them. Didn't even know anything was amiss until I realised what was gone." Again, that pained look. "Oh, I don't mean to trouble you, my dear, but if you don't mind my saying it just once to get it off my chest – it's just about broken my heart."

What was especially troubling Crowley was how they could have even gotten in without Aziraphale knowing. What if it were one of the angel's lot? Or, worse, one of his own...

Yes, what if the culprit was a demon?

"What exactly did they take, angel?"

"A rare copy of The Extremely Big Book of Astronomy."

Crowley felt his cheeks grow hot. "Er, about that..."

But Aziraphale had gone glassy-eyed and was talking about the book as if he were trying to sell Crowley on how simply amazing this lost treasure was. "Full glossy pictures, and a certain typo in the index which makes it an exceeding sought-after..."

Typo in the index? That was all? So it was worth something because it was defective and shitty? Well, then again, the same could be said for most of the Bibles in the shop, too, but those at least were old.

Whatever. It didn't really matter. Crowley's mind rushed back to the matter at hand. The thief had been a demon, after all. Just not in the way he'd feared. "Ugh, stop. Listen to me. You haven't been robbed. I took it. Last night. I picked it up on my way out."

"You?" Aziraphale gawked at him in confusion. "But why?"

"To be fair, you always said I was allowed to peruse the shop for something to read if I wanted. And I didn't know it was valuable."

"Good heavens." His face had become unreadable. "Well, that's certainly the last thing I expected."

"I only borrowed it," Crowley felt the need to say, defensively. He had figured he didn't need to ask, since he was coming back this morning. "It's in the Bentley now – I'll get it for you."

In moments, Crowley had gone and returned with the book and was placing the large, heavy volume into Aziraphale's elegantly manicured hands. The angel's fingers tightened protectively around the book as if from instinct.

"Why did you take it?"

"I told you – I didn't know it was valuable."

"My dear, I don't mean that. I meant..." He smiled. "I never knew you were interested in astronomy. What's touched you so?"

"Reminded me of old times, I suppose." The demon folded his arms across his chest and shifted uncomfortably from one foot to the other.

"Oh?" Aziraphale's brow lifted. "Oh. Were you...? That is, you didn't...? Did you make some of these?"

He shrugged, with awkward modesty. "I helped."

"Show me one you made." He opened the book to the title page, set it on the desk, and dragged Crowley over by the arm despite the demon's vehement protests. "Please. I want to see."

Reluctantly, Crowley flipped a few pages and tapped the picture of a nebula.

"That's beautiful," breathed the angel, his reading spectacles perched atop his nose, sliding down the bridge as he squinted eagerly. "You did that? Good Heavens, how extraordinary! I never knew!"

But talking about any time before he became a demon made Crowley uncomfortable and prickly. "I'd prefer it if you acted like you still don't."

"But Crowley–"

"See, this is why I didn't ask to borrow it."

"Very well." Aziraphale held up a hand mercifully. "I'll stop. Everything's back to how it was, just tickety-boo."

"Right. As you say. Tickety-whatever."

And it was. Except for the fact that Crowley, who had removed his sunglasses, hadn't taken his yellow snake eyes off the book. He tried to make himself stop looking at it, didn't want Aziraphale to see how much he wanted to keep it.

He was not in the least successful.

Out of pure desperation, Crowley decided to bail entirely. He couldn't even remember what they'd had planned to do today, why they'd met up here, and he was already blurting out goodbyes and flinging himself out of the shop before Aziraphale could remind him.

It was unlike him to be so harried, that was far more the angel's nervous demeanour, but he felt a more than a little vulnerable after showing Aziraphale that stupid bloody nebula.

Aziraphale watched Crowley from the window. He looked down at the book on the desk, then at the demon's retreating back.

The angel's fingers wrapped around a fountain pen.

A couple minutes later, when he'd written what he wanted to, he flicked a beringed little finger in the direction of the book and it vanished.

Crowley was astonished to discover The Extremely Big Book of Astronomy resting on the passenger seat of the Bentley.

Was he going mad? Had he, or had he not, just returned that damnable thing to Aziraphale?

Some nagging sense buzzing at the back of his head possessed him to open it and look at the flyleaf.

There, in sickeningly neat copperplate handwriting, was a little inscription that hadn't existed the night before.

To Crowley with Agape,

We're All God's Creatures

– Aziraphale

A/N: Reviews always welcome, replies may be delayed.