"...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.