"...sorry." Ted goes back to poking numbers, grumbling to himself about the unfairness of the universe for presenting him with insane wizard physics. 

"Nonmagical alternatives, huh. Well it's probably better than quitting my job, my poor NEWT students. Miss Pomfrey, what happens if wizards take Muggle potions?" 

"What happens?? Professor Weasley no offense but that's an insane question. Especially if you don't even know which potion. Absolutely anything could happen." 

"... right, going to follow up with you on that idea later," he says to Ophelia, because they literally just now learned an important lesson about apparently harmless personal facts around friendlies who do not strictly absolutely need to know them. "Meantime... sounds like maybe we might want to know... which people might want me dead and are an unusually small number of social steps from both the Vectors and me?" He says this with the mildly despairing tone of someone who both hates that kind of thing and is terrible at it.  

Nelya, who enjoys that sort of thing in theory and is also well aware she's terrible at it, heroically refrains from saying "oh no" out loud. 

Cedrella rolls her eyes fondly and then grins at Ophelia. "So have you got a network chart yet or are you more of a memory palace type?" 

"Not one that reliably covers the upper years in any case, but I do have some information.  ...The birds may have more, or rather different, information than I."

She turns towards the one that's still in the room, and gently impresses a thought more complex than she can convey with birdcalls.  There will be bribery, if the flock visits her and consents to sharing memories so that she may trace recent interactions.  (There is, of course, also bribery for carrying that message.)

"...I do as best I can to remember anything that could possibly be useful myself, but as the mind is a fallible tool I do prefer to write things down.  One moment, please."

She produces a book that is surely not the copy of Hogwarts: a History it is presently pretending to be, and pages through it.  (It's actually a 'birdwatching' journal, underneath the somewhat hastily Transfigured cover.)

"The birds?" 

Cedrella watches this exchange in fascination. 

"Clever. Now I'm terribly curious what Kettleburn is going to make of you." 

(Septimus was aware that Ophelia has a secret birdwatching journal. He thought she was just hiding it because that is an embarrassing hobby, though. He is vaguely bewildered to discover it evidently has secret scheme function? Which his wife understood immediately on looking at it?? Slytherins are truly such a way.) 

"Corvids are a terribly clever genus before you consider the influence of magic on their intellect," she opines almost idly as she riffles through the most recent pages.  "...I'm going to need to replenish my bribes," she continues, as she fishes out various bird-friendly snack foods, "but considering the need, it's surely worth the cost.  They won't know everything, but they do recognize faces.  And sounds, for that matter."

And here they come.

Now what can she gather from their knowledge, and her own?

"...Realistically, tracing the flow of knowledge of this vulnerability is going to be all but impossible with how patchy our ability to surveil is, but if we can find anyone sneaking around Nelya - surely they'd have had to - then we might be able to pin down our culprit.  That said, Madam Weasley, if you want to work with your husband and see if you can figure out who could have known that information...

"Well, a shot in the dark is still a shot, especially if we can compare notes."

HmmmMMmMmmm. Can she sincerely claim to Arcturus to have just been terribly charmed by the corvids and definitely not been additionally motivated by the expected negative impact on whatever Narcissa and her evil but technically-by-the-rules-very-reasonably-selected fiancée are up to. 

... the corvids are really very charming.

"I'll investigate and get back to you."

What comes next? 

Bribery!

Legilimency.

There are a vast variety of things happening at Hogwarts at all times and it is hard to say how they are related even with extensive diagramming.

Some of them might even be relevant! Who knows! 

...Hm.

1) She rather thought she'd left a better impression on Professor McGonagall than that, but - ah.  Professor McGonagall presumably does not know that Narcissa Malfoy has been tricked into believing that Ophelia Prince is hers.  Do pass that along, please, this sort of misunderstanding really can't be permitted to continue.

2) If there exists a countercharm for Obliviation, someone must cast it upon Nelya Vector.  She's fairly confident that Nelya was Obliviated in addition to being otherwise tampered with.

3) (Why on earth are the wards not set up to scream loudly if someone attempts to cast Obliviate within them, nobody should be Obliviating people inside Hogwarts.  Honestly she thinks it ought to be Unforgiveable, except for all the reasons that wouldn't work out.)

4) Madam Augusta Longbottom is terrifying.  But she doesn't actually suspect this to be internal strife amongst the anti-Death-Eater paramilitary that totally doesn't exist.  Surely someone would have just told Septimus to knock it off?  This sort of backstabbing just seems uncharacteristic.

5) She finds herself circling the Rosiers contemplatively.  Whether or not they were involved directly she thinks that if the plot was Death-Eater driven (and she thinks it most likely was), they would have been well-positioned to pick up something about Nelya from Hex.

6) None of this explains how anybody found out about Septimus's medical conditions to be able to formulate the explosive.

7) She needs to know more about the upper-years' specialties.  That sort of ability to sabotage a Runes project can't occur across every single student.

7a) Nor can the requisite Charms and-or medical knowledge.

7b) Which means that if the plot originated entirely from within Hogwarts, identifying the confluence of those skillsets would permit a drastic narrowing of the suspects list.  It cannot, however, be assumed that this was entirely the case.  Someone inside Hogwarts might have reached out for advice from other sources.  Still, that would narrow things down...

Other thoughts:

That mess with ?Brutus's Relative's Auror Partner? that she should have the name of somewhere in here is probably not necessarily...

Oh hell.  It might be.  She still hasn't figured out a more plausible method for the leak of Septimus's medical information.  Someone who has a family member with a similar condition?  But would they know?  Someone who has - no, they couldn't - oh, but if they Confunded Nelya into doing it they wouldn't have had to touch the paper, and mania is like that -

There's only more questions.

Also the Incredibly Suspicious Murder Investigation't is rather concerning in its own right!  Who would benefit from covering that up?

(The thing with Ted and Septimus seems very obviously like either a staged or real fight about training vis-a-vis How To Survive Duelling Arcturus Black, at least, and while she's going to double-check with them, she doesn't think it's related to the murder attempt.)

(Though perhaps she should have been less quick to rule out...)

(...no.  No, that doesn't make sense at all.  It's not the Blacks.  That matter was surely settled.)

(But it could be that Narcissa has more information about Septimus than she originally thought she would.  But she's still pretty sure that anyone who could've had information from Narcissa inform their plotting, would have known that Narcissa is at least somewhat invested in her.  And maybe they took that risk, but why?)

...Gods, she hopes there's no coded conversations in the Quidditch stuff.  Quidditch is.  Such.  A sport.  She wants nothing to do with it.  Why is the Snitch like that, for crying out loud.  150 points and the end of scoring is just beyond the pale.  Make it worth five.  Maybe twenty-five, but - for the love of balance, not 150!  Why are Bludgers!  Are broken bones just good clean fun around here?!

(But she doesn't actually think there's someone passing coded messages through discussions of the local Quidditch.  Too easy to notice discrepancies.)

(It is also interesting, but likely completely irrelevant, to note that Augusta Longbottom plays wizard chess against a Malfoy enough for her set to have opinions about theirs.)

(...Say.  Madam Cedrella.  Could you invisibly lurk in Ancient Runes and-or Arithmancy classes (as relevant) and feel for if anyone spooks when they see that explosive revealed as an extra-credit reverse engineering project?  She'd do it herself but she's pretty sure she has scheduling conflicts.)