Waugh. That's so valid but nooooo she doesn't waaaannnnnna-- 

that your skills were turned against you

Wait, what. 

Puzzled blinking. "That my skills were... I mean, yes, right, that's what happened is my own shield charm got me...?" Hmm, no, she obviously means something else, what would Nelya's wand know about this that she wouldn't, if the door asked her a riddle that goes what is impossible for a wizard to know, but impossible for her wand to forget--

".....ooooohhh. Hate that. Can you cast it?" Otherwise she'll have to... borrow Pancha's wand probably. Which she can do but ugh ugh ugh it's like touching soap without gloves on. 

"I can, yes."  And she will, gently, leaning into the spell with her Legilimency enough to hopefully communicate just what she's asking Nelya's wand if it remembers.

Wands look incredibly weird to psychic senses. 

The reason for this is mostly that they are much more like trees than like human(&c) people, and trees are a pretty weird type of guy. However, it's also, a little, that they're more like seers than like any other type of people, and seers experience the world a little bit differently than everyone else. Wands look at a person as they [can be|might be|already are going to be], when they're choosing which wizard is theirs, more than they are looking at a person as they [are|have been], and this is also the sensory modality through which a true seer observes reality, when they look from the right angle. 

Nelya's wand thinks that, uh, 

[confund|obliviate|imperius] [self|wizard|beloved|great work] [is|will be|might] [likely|possible|sometimes] [because|therefore] [distractible|forgot|skilled|(trope-wizard-bad-at-politics)]? Errrrrrr hang on hang on no that first one is too many things. [obliviate|forget], it knows this one. [is|will be|inevitable] [again|repetition|familiar]?? 

The concept of 'the past' is kind of confusing for wands. This is why there's a whole spell for formalizing it for them! 

Normally a prior incantato will time out after, like, ten spells, at best, regardless of the skill of the caster, because wands themselves are not particularly cooperative with this annoying task. However, this one has been notified of exactly what is going on and why, and is trying very hard to remember.

Prior Incantato returns: quillsharpen - quillsharpen - inkspill clean - (series of dozens similar innocuous dailies) - shield (wrong) - shield (wrong) - timeclock - timeclock - light - light - light - light - light - light - 

and then it runs out. 

Nelya squints between the gleaming spell echoes as they fade out of the air and the perfectly functional ambient library crystal lights. "Well that's. Incredibly suspicious, isn't it." 

"...This is, very technically, a null result, I think," in that she can't immediately see it having proved or disproved anything...

"But I don't like it either."

"Not to mention what I observed on secondary channels."

Did those timekeeping spells show what time they were showing, at the time?

"Can you place any of those last spells before those earliest two shielding - charms!

"Multiple!

"Which you most definitely would have noticed happening twice!

"So it wasn't you who made you forget, I think.  Because that would have been in the chain between those two.

"And there's only so many people that are known to have the capability, though considering that Slytherin does love its self-studies on certain subjects, it's not impossible someone else could know how to cast Obliviate, outside of normal channels of learning...

"Still, it narrows the pool of people who could have been responsible for this.

"And it means we can be reasonably confident that this happened shortly before you met with Professor Weasley.  You would have cast something in a class or for utility purposes between them, otherwise.

"So the question is how and where you were caught out.  Where were you, last, before you went to Professor Weasley's office?  Do you recall?"

And if it's the library, she might be able to crosscheck that with Madam Pince...

Gazing thoughtfully at the wall, trying to reconstruct the evening. "...I think I did cast it twice that I can remember. It was wrong differently but that's why-- I was here in the library, trying to get it to work, and I was checking the time every, every," amount, of time, what the hell, "unit time I can't remember? because Tri kept forgetting to sleep his exam week and I was trying to not end up in the hospital wing, ugh, look how well that worked out for me, and it was still wrong, and that's why I decided to go ask Professor Weasley... but it was wrong like it was a perfectly good shield charm and just wasn't doing the new efficiency thing, it's only the second time it exploded. Can't have been that long between them, though, yeah, I think that last timeclock had to've been late enough that when I tried it again and it still didn't work I was like 'oh man, gotta go over to Defense right away before it's curfew'?" 

"...Well that's not a suspiciously specific vagueness at all."  She doesn't suppose that those time charms showed what time they were cast at, in the wand's recollection?

And would the normal operation of the library produce any records or memories of when and with or after whom Nelya exited?

The wand does not remember any such thing but the librarian's meticulous records do! 

Madam Pince is, to the surprise of various Vectors, quite willing to show Ophelia her records. (Ena Vector, the eldest, may perhaps once have spilled a smudge of ink on the corner of one (1) book. Most Hogwarts students manage to annoy the librarian in at least one such way, or be obviously related to someone who did in the last ten years, by the time they've been there a week, because she is very easy to annoy. Ophelia Prince is in the habit of using the library very politely and respectfully for its intended purpose, i.e., in pursuit of knowledge and not just to do her homework, while taking great care not to damage the books, and also she invented a charm for doing it even more quietly. She is the librarian's favorite student.) 

Nelya Vector, on the day of The Incident, checked out the following books relevant to her project, at precisely -

That's actually about two hours before The Incident. It does not take that long to walk from here to Professor Weasley's office. 

Oh dear.  And the timekeeping charms didn't tell her when they were cast, either.

"Well, that's not a good sign, but we already suspected tampering, so that's not new.  It does localize the 'when' further, though..."

Who else was here that evening?

"...Nelya, if we assume for the moment that you were going to test-cast your shielding charm, after leaving the library, where would you have been going from here, once you left?  And where would you have been going if you hadn't been planning to do that?"

All her answers lead to more blasted questions.  She's going to have to ask Lily for help with the portraits.

...Or try using Legilimentic communication on a building.  It seems to have worked on wands, so why not.

Decisions, decisions.

"Like instead of asking Weasley?" Aw man a social counterfactual. Terrible. Modeling her own brain is easier than other people's but still. "Errrrm.... well, Spellman's policy says if you want to do Real Testing instead of Model Testing(1), then you are supposed to wait until study hall hours and reserve a test circle slot, but if you gotta(2), you go to the Quidditch pitch?" And Nelya is generally in the habit of Following the Rules. 

(1) I.e., actually casting a spell you aren't 100% sure what it does, rather than 3d-diagramming it, which wands struggle a little to tell the difference between because the latter is sort of like casting it with zero power. 

(2) It's not, like, a great idea to encourage sleep-deprived teenagers to go outside in the middle of the night when the Forest is Right there, but the Runes professor has had to clean up after truly so many midnight explosions over his tenure and he has learned that you cannot stop the sleep-deprived magic teenagers from making insane choices but you can at least encourage them to do so in a manner less likely to seriously injure their roommates. 

She nods.  "Is that something that you'd have done?"

"Depends if there's a practice on." Which is definitely the only and totally non-embarrassing reason she keeps track of the Quidditch practice schedule. "Don't think there was that day so... I'd say yes except, observably..." 

Why didn't she go hang out on the probably-empty Quidditch pitch stress-testing her broken spell to figure out what was wrong with it. 

"...I guess I decided that didn't work any of the previous times and I'd better try something different if I wanted to meet my deadline?" she hazards, a little uncertainly. "But yeah, would have been a normal thing to do." 

"...I think that maybe you did go to the Quidditch pitch, actually.  Outside the castle's interior wards, relatively isolated...  If I was planning to turn a student into an assassination attempt, which I do not have any desire nor ability to do, I'd much rather lure them outside and try there than figure out how to trick Hogwarts.

"And you were going outside often to test things, I'd imagine."

...Habits, it is often said, are dangerous things to have.

"So if someone had been looking for a plausible target...

"You'd fit the profile."

Oh. 

:( 

"... what, uh, do we... do... with that information."  

"I think at this point I take all this back to Professor Weasley, and you maybe start a trend of not going out to the pitch alone."

"...right, okay," this is going to come up like once tops in the next two weeks until graduation but she would feel so dumb if she got a specific rule to follow to not die and then died of doing it wrong, "uh, how alone is a problem exactly? Like a lot of the time when I'm there, there's also a couple guys running laps or doing drills or whatever, I'm not the only person around here with habits." Thoughtful pause. "I will admittedly grant you that I am probably way easier to jump than Lynch and Maddock, though, yeah. Whoever tried would simply die of being punched in the face, can you imagine." Mildly self-conscious giggle. 

"I would want a second person I know well enough, who's close enough to help if a spell explodes.  But the joggers might not be horrible, either."

It's a shame Ophelia is right that that's probably not really good enough because getting heroically rescued from some sort of unidentified Slytherin bullshit at a hundred yards by the hottest Gryffindor ahem the one who happens to usually be about a hundred yards away for reasons totally unrelated to her scheduling choices, would be so romantic,, 

"Right. Yeah." Nod nod. "I guess let me know if you need anything else? And good luck with the... Slytherin...ing." 

"Thank you.  I will.  I hope the Arithmancy treats you kindly.  If anyone asks, I had a question about the Arithmancy of, a thing I can do, that I'd like to formalize as a noise-dampening charm.  ...Which I should probably actually ask, so you won't be lying -"

The conversation, at this point, likely devolves into more spell theory than this author's brain can handle.

Nelya would be thrilled to help with that! 

Eventually she returns to her project, and Ophelia is free to proceed to the next task in her queue. 

Right.  Next steps:

1) Tell Professor Weasley her suspicions.

2) Find out whether there's any information available on who was out on the Quidditch pitch between the time Nelya left the library and the incident happening.