I couldn't choose between writing a Good Omens fanfic or a Harry Potter one, so I'm writing my first crossover! This will probably be a bit crap, but it was fun to write.

There was a small note lying open on the desktop in the backroom of a shabby bookshop in Soho. It was a summons to heaven. Aziraphale felt his gut clench at the site of it. Heaven hadn't contacted him since they had tried to put him to death last year. Since then, he had gradually learnt to stop the tingles of paranoia every time the post came. Every letter could hold the new that they had figured out he wasn't really immune to hellfire, and that they were coming back to finish him off. Clearly, he had taken his safety for granted. They knew. He was going to die for sure.

…

"Just don't show up angel," Crowley suggested, "I've done it loads of times."

He was sprawled on the sofa in Aziraphale's bookshop, looking unconcerned as Aziraphale panicked wildly.

"I can't," Aziraphale responded absentmindedly, pacing the room, which was hard as there were so many bookshelves around and he had to slalom, "they might know about what we did. If they do, we're both in danger. I have to find out what it is."

"Fine," Crowley scowled, "give them what they want. But angel," his expression softened slightly, "We can swap again if you like. You know, just in case…"

His voice trailed off, an indication that maybe his relaxed stance was not all that it seemed.

"No," Aziraphale said, "I'm going. I'm not going to let them terrify me anymore. I'll be back, don't worry."

Crowley gave him a look which said, 'I never worry'. It didn't quite meet his eyes.

…

Aziraphale had never seen Gabriel look so uncomfortable. The usually confident angel's violet eyes were shifting uncomfortably as Aziraphale took a seat opposite him. Clearly he hadn't forgotten that the last time they met, he had told Aziraphale to 'shut up and die already'.

"Hello Gabriel," the angel said, slightly stiffly, but nonetheless with his usual politeness.

"Aziraphale," Gabriel nodded curtly in reply.

"If I may-" Aziraphale started, but Gabriel cut him off.

"You want to know why you are here."

"Well, yes." Gosh this was awkward.

"Heaven would like to, er, enlist, your services," Gabriel explained, "not as an angel," he added hurriedly, "but we, we need your help."

So that was why Gabriel looked like he was sitting on something pointy. It is never an enjoyable experience to ask someone for help after you have shunned them and sentenced them to death.

"As what?" Aziraphale asked apprehensively, "If not an angel I mean."

"As a, er" Gabriel searched for the appropriate word, "guardian, if you like. We would be willing to, overlook, your actions during Armageddon if you complete this task for us."

"Why me?" Aziraphale asked, baffled.

"You have been on earth for years. You- well, you blend in," Gabriel explained, "And we need someone to keep an eye on things at a certain school."

Aziraphale still looked confused, but he hadn't refused yet, so Gabriel ploughed on.

"There's a child, starting at this school later this year. But he's in danger and we need you to keep an eye on him."

"Why is he in danger?"

"I trust you've heard of Harry Potter."

Gabriel sounded rather exasperated now. Why couldn't the angel just accept the task? What was the point of all of these questions?

"Yes," Aziraphale went white as the truth dawned, "He's going to Hogwarts, this year? And you want me to keep an eye on him?"

Now that Aziraphale understood his task, Gabriel gave up trying to convince him gently. Tact had never been the angel's strong point.

"So, you'll do it. Thanks a lot. We're all rooting for you."

With a cheery smile of someone who has got a difficult job off their hands, Gabriel ushered Aziraphale out of the room. In heaven, they outsource these things.