A/N: AO3 Chocolate Box exchange gift, inspired by a prompt for Mary Poppins & Granny Weatherwax & Minerva McGonagall. Set after the Discworld novel Equal Rites, with mild spoilers for that story.

Hogwarts Needs Substitute Teachers

When Granny Weatherwax returned home from Ankh-Morpork, she didn't expect to hear from anyone at Unseen University. Yes, there'd been a suggestion that she might return to teach, but she thought they'd forget all about it once she left. Most people were like that, too busy with what they were doing in the moment to give much thought to the past or future.

To her surprise, a few months later she received a letter from the Archchancellor. He'd recommended her for something called Hogwarts, and said she should set a fire in her hearth at noon the day after she received the letter to learn more about what they needed from her.

At the specified time she had a fire roaring, and the flames took the shape of a face. "Greetings, Esme Weatherwax," said the voice from the fire. "I am Professor Minerva McGonagall from the Hogwarts School of Witchcraft and Wizardry."

The face and voice seemed normal enough – allaying her initial fears that this could be a demon – and Granny approved the choice of a traditional black witch's hat. "This Hogwarts is a school? Last year one of my goats had warts that looked something like hogs."

The woman in the fireplace chuckled. "My grandparents raised goats, and I recall that caring for the animals was not a task for the faint of heart." She removed her hat, revealing hair pulled back in a bun. "Esme, the reason I've contacted you is that Hogwarts has a desperate need for instructors. As you can imagine, teaching magic is an inherently dangerous task. The slightest lapse of attention or moment of distraction in the classroom during a demonstration of our craft can lead to harrowing results. We have two professors in the infirmary recovering from magical mishaps. Another has contracted a nasty virus, and one more has requested a leave to deal with a family emergency. If you can join us for the next week or longer, we would be immensely grateful. You came highly recommended by Archchancellor Cutangle. He said you've mastered something called Borrowing, which sounds related to my area of expertise. I teach Transfiguration."

An hour later, Granny stepped through a portal onto the grounds of Hogwarts and joined two other substitute instructors. Another arrived moments later, floating to the ground with an open umbrella in one hand and a carpet bag in the other. Granny had to admit that flying by umbrella looked more comfortable than sitting on a broom.

A wizard led two of the instructors away, and Professor McGonagall asked Granny and the woman with the umbrella to follow her to a classroom, where they would discuss their qualifications and lesson plans.

On the walk, the other instructor introduced herself as Mary Poppins. She wore a black hat with flowers and cherries on it – not particularly witch-like, but Granny rather thought she'd enjoy something similar for a day off. Once inside the classroom, Mary set her carpet bag on the desk and pulled out a hat stand. She placed her hat and coat on the stand.

Granny sniffed.

"Do you have something to say?" Mary asked.

"I know a show-off when I see one." It wasn't normally a trait Granny admired, but sometimes you needed to do something big to make people take you seriously. "It's all down to headology. Young thing like you with rosy cheeks and that sweet face, you have to make to an impression or the students won't mind you."

"They'll mind me when I show them how in every job that must be done, there is an element of fun." Mary sang the last bit. When she snapped her fingers, books that had been scattered about the room flew to the shelves.

Granny wasn't going to admit to being impressed. "Headology again. That works for the littlest ones, but an older child needs to accept that hard work is part of life."

The professor spoke up. "You feel their reward is a sense of a job well done, Esme?"

"That's all the reward most people will get."

"Hmm. Rather a dour outlook." Mary pulled a tape measure from her carpet bag. "Stand still," she told Granny. "Let's see how you measure up." When she'd taken Granny's measure she said, "As I suspected. Extremely stubborn and suspicious."

"And what's your measure?" asked Minerva.

"Esme, would you hold the tape?" Mary requested. "Yes, precisely like that." She held her finger at the mark, and read, "Practically perfect in every way." Then she blinked in surprise. "And a little cheeky."

"What was your last position, Mary?" the professor asked.

"I was a nanny for two children, Jane and Michael Banks."

"Why'd they need a nanny?" Granny wondered. "What happened to their parents?"

"They were very busy," Mary explained. "Mr. Banks was a banker, and Mrs. Banks was a suffragette."

"What did she suffer from?"

"A lack of women's rights."

"I saw a lot of that at Unseen University." Granny rolled up her sleeves and walked over to an owl perched in a corner of the room. "I don't have any treats for you, but I'll bring something tomorrow if you'll let me Borrow you now. I promise when the students are here I'll teach 'em to respect their hosts for Borrowing."

The owl gave a slight nod, and then Granny picked her spot. "Thanks for clearing away the books," she said to Mary as she stretched out on a table.

"Taking a nap. This is teaching hard work?" Mary asked.

"From what Esme described," Minerva explained in a hushed aside, "she can borrow the mind of any living creature. She'll share its knowledge and experiences, and can influence its actions to some extent."

"To my way of thinking, it's simpler to Borrow a creature than to turn into one. That's the best kind of headology, where you do something simple, but to the average person it looks impossible," Granny said. "Get comfortable as you can in these chairs, and each of you take one of my hands." When they were in position, she reached out to touch the bright silver mind of the owl.

Mary and Minerva gasped as the owl took flight.

Granny smiled and did a little showing off of her own. For twenty minutes they explored Hogwarts from above. When she opened her eyes, she took a moment to orient herself before sitting up.

"Couldn't we have continued a little longer?" Mary asked. "Those trees along the lake looked particularly inviting."

"Too long or too many times, and you'll get a craving for mice," Granny warned.

"With a spoonful of sugar," Mary suggested, "that mightn't be too bad." She stood up, forgot she wasn't an owl, spread her wings to fly and fell onto the floor.

Minerva looked at Mary Poppins with concern, and then turned to Granny. "I suggest you limit Borrowing to five minutes at a time when the students are participating."

A/N: It was such fun to write this treat! I like to think the other two substitutes were an elf from Tolkien's works, and Groot from Guardians of the Galaxy.

Thanks to Silbrith for working her beta reader magic!