One day in July Aunt Petunia takes Dudley to London to buy his uniform and leaves Sarah at Mrs. Figg's, who seems to have lost some of her erstwhile fondness for her cats given that she broke her leg tripping over one.

That makes some amount of sense. Mrs. Figg has always be nice to her so she tries to be as helpful as she can.

She's such a darling. Yes, she'd love some help, and here, have some chocolate.

(Which tastes like it might be a hundred years old.)

Well, she'll eat it anyway, she's eaten stuff which was much less tasty.

She is such a charming, helpful young lady, and Mrs. Figg is sure to tell her uncle and aunt this when she returns home.

That evening, Dudley parades around the living room for the family in his brand-​new uniform. Smeltings' boys wear maroon tailcoats, orange knickerbockers, and flat straw hats called boaters. They also carry knobbly sticks, used for hitting each other while the teachers aren't looking. This is supposed to be good training for later life.

That sounds like the sort of thing an insane person would come up with. She very carefully doesn't share this opinion.

There's a horrible smell in the kitchen the next morning when Sarah goes in for breakfast. It seems to be coming from a large metal tub in the sink.

What fresh horror does the Dursley household have in store this time? She wrinkles her nose at the smell but as usual asks. "Do you need any help Aunt Petunia?"

"No, don't touch those, they're to be your uniform."

"Alright." It takes a lot of effort not to roll her eyes at that. For all their dislike of abnormality the Dursleys go really far out of their way to not spend money on her.

Dudley and—

—Uncle Vernon come in, wearing identical expressions of disgust. Uncle Vernon opens his newspaper as usual and Dudley bangs his stick on the table as he's been wont to do lately.

She'll just eat her breakfast and try to stay out of the way.

When breakfast is they hear the click of the mail slot and the flop of letters on the doormat.

"Get the mail, Dudley," says Uncle Vernon from behind his paper.

"Make Sarah get it."

"Get the mail, Sarah."

Sarah gets up and walks down the hall to get the mail.

Three things lay on the doormat: a postcard from Uncle Vernon's sister Marge, who's vacationing on the Isle of Wight, a brown envelope that looks like a bill, and—a letter for Sarah.

Well then, she'll try sneaking that into her cupboard on the way back to the kitchen. No time to think about that now.

No one spares her a glance after she delivers the mail.

"Marge's ill," Uncle Vernon informs Petunia. "Ate a funny whelk..."

When she finishes her breakfast and some of her chores she'll go to her cupboard and open her letter.

The address says:

Ms. S. Potter
The Cupboard under the Stairs
4 Privet Drive
Little Whinging
Surrey 

It contains two pieces of parchment, folded neatly.

Hm, that's weirdly specific. She unfolds the parchment.

The inside is just as fancy as the outside, written with green ink. The first page reads:

HOGWARTS SCHOOL
of WITCHCRAFT and WIZARDRY

Headmaster: Albus Dumbledore
(Order of Merlin, First Class, Grand Sorc., Chf. Warlock,
Supreme Mugwump, International Confed. of Wizards)

Dear Ms. Potter,
We are pleased to inform you that you have been accepted at Hogwarts School of Witchcraft and Wizardry. Please find enclosed a list of all necessary books and equipment.
Term begins on 1 September. We await your owl by no later than 31 July.

Yours sincerely,

Minerva McGonagall
Deputy Headmistress

"Well then." So the strange things she can do are magic and other magic users want her to go to their school. She isn't sure how she's supposed to get back in touch with them though. She carefully hides the letter beneath her bed and goes looking for paper; she doesn't know how to send a reply but she can at least write one.

Dear Professor Mcgonagall,

I would like to attend your school but I am uncertain where I would obtain the listed materials. Would it be possible for a member of staff to meet me to discuss?

Sincerely,

Sarah Potter

Then she folds the letter and hides it in a pocket and goes outside. Are there any owls hanging around?