This was a great story and perfectly sets up Dumbledore trying to use the resurrection stone before getting cursed.

that was amazing

seven is like an important magical number I think

"the riddle was unsolvable" ? Uhm, no it wasn't.

When they mentioned the Philosopher's Stone coming to Hogwarts in 1991, I knew it had to be Albus and that mirror. Funny coincidence that she still left after the same amount of time.

"I am not sure that I would trust him with the knowledge that our dreams and sorrows can step out of an enchanted mirror and into reality, if only for a few brief moments."
Would've been 'burden' rather than 'trust', I feel. Thank you for not making Snape into some monster, even if you did insult his sense of logic :-)

Hahaha, what a fitting ending with the Pensieve!

I only realized just now this story is a decade old, sorry for my detailed comments wrt typos and stuff as you probably don't care about it now!

Thank you very much for writing this clever, intriguing story, I enjoyed it a lot! You had more stories about Sally-Anne, you said? :-)

"Maruders' Map"
"more complex magic that a chocolate frog card;" than

Did they influence this reality so much that Snape and Lupin visit a pub together and have a half decent conversation? Whoa... (I'd say weird to do this here instead of in one of their offices at Hogwarts, but then the same can be said of Dumbledore holding job interviews)

"Finally he understood who Sally-Anne Perks had been"
Well, you have me very puzzled...

"No, in in the Hog's Head pub"

O...kay... Did someone make Ariana manifest as Sally-Anne?
One of her brothers? With some Dark ritual of some sort? Snape let them off easy and giving points is so unlike him, and now I wonder if he'd enjoy the mystery and contribute some ideas...

"1865" No, 1896!

"Not even the unsuitable young man I had three awkward dates with in 1942 (...) Tom Riddle."" Lol oh jeez, you really do tie every single loose end together, don't you! XD

Now that took a turn I hadn't expected (despite my previous comment). Ariana never made it to Hogwarts, but what if she did - and we know she has a portrait. Clever you :-)
Though now it's strange the Sorting Hat didn't remember Ariana's name; if she had been Sorted before, why not focus on erasing other details about her but keep the name? Wouldn't that... be less noticeable?

"Juts to make sure"

Ron Weasley
Peter Pettigrew
If the names are on top of each other like the dots, you should still be able to read 'ew' - very fitting! XD

Haah, they can rewind the Map, that is awesome.
Ron and Harry talking to Malfoy in the Slytherin common room happened during the Christmas holidays though.

The Map recognizes Peeves and trolls (aren't there trolls at Hogwarts now too?), but not Sally-Anne? I'm miffed on her behalf XD

"gradual change came over her; a sadness began to grow within her, and she spent more and more time in the bathroom crying. And then one day"
...This suggests far more time to me than just one measly week though

'How can this be?' Did she just reappear 95 years later? Did she manifest in two times at once? Well, not if she already knew the way...

Hahaha, of course now Ron finds a card he didn't think existed... At least he's coming around. You'd think he'd believe Harry after finding out the mystery voice Harry heard was a very real Basilisk...

"no record in the Muggle archives of a Sally-Anne Perks born either in 1980 or in 1885"
Yeah, so, as implied, I had to look up Somerset House and found it houses the National Archives, but also found that birth records are kept in the General Register Office instead (is that in Somerset House too?) and - the reason I got curious in the first place - birth records are indeed only public if they're older than one hundred years bc privacy. So realistically, the Grangers could have found the first Sally-Anne in the GRO, but not the second.

"Peeves told me once of a magical map of the school, fashioned by a band of students long ago"
Surely a mere two decades is nothing in this company, so... second mystery: was the Marauder's Map not the first of its kind?

"Unless, of course, you had been robbed of your soul and your name..."
As in, Dementor's Kiss?

""Password? she asked testily." Quotation marks missing (maybe they're with Sally-Anne?)

Oh my, so wizards were far ahead of Muggles in painting style then.

"Harry was confused.
The portrait sighed a little, obviously realizing that she had overestimated his intelligence." Lol - go start a therapy group with Snape
(Now I'm wondering how much dirt these portraits and ghosts have on the current teachers)

Hogwarts itself? Well, it IS sentient. Did it murder her with the staircases? XD
Bit difficult communicating though...

Lots of hints from McGonagall, that's nice and unexpected. Usually Dumbles is the one to encourage while pretending to do the opposite. Really curious where this is going! XD
(And: was there ever another Sally-Anne? People do get named after relatives as well.)

'Somerset House' is not terribly informative for non-UK readers btw... There are more issues, but you may have addressed those in the next chapter :-)

Whaaaaat? The plot thickens. Was she a lost time traveller or something?

"Sirius must have been framed in some way" Yes. By another Gryffindor.

I wonder if the Sorting Hat remembers her. Or Ollivander.

What a very intriguing idea! I love that someone noticed that name and decided to do something with it. There's also The Best Revenge by Arsinoe de Blassenville in which she's a talented ballet dancer who gets into Juilliard or something at 12, but I prefer murder mysteries :-)

"Sally-Anne Perks had been at Hogwarts for seven days, before vanishing into thin air. What had happened to her during those seven days?"

This - sorry - made me laugh: seven days, huh? Did she watch a mysterious videotape and then get a phonecall the morning before she left for Hogwarts? XD

I've seen people recommend this story several times over the years, but for some reason, I never bothered to read it before now. I enjoyed it a lot, but I am confused about one thing that never got an adequate answer: Why did Harry remember Sally-Anne to begin with? I know Hermione speculated that it was because his mind was different (presumably the horcrux had something to do with it), but that seems like a very unsatisfying answer. Was it because McGonagall chose to let him keep his memory in the hope that he would uncover the mystery?

Oh, and one other thing that was less of a mystery and more of a "why didn't they think of that": I'm surprised they never considered the diary!Tom Riddle that Harry met in the Chamber. As I recall, he described himself as a memory and was apparently trying to come back to life, so there are some clear similarities to Sally-Anne's situation. Obviously it wouldn't have gotten them anywhere, but they wouldn't have known that, so I don't know why it never came up.

Anyway, the story was great, and I enjoyed reading it.