Hello! I'm so glad that you re-requested, because I've been itching to read more of this story but have been beating back other obligations to get to it. I'm really eager to read more. :)
Omg. Omg, she DID jump. Of course she jumped, but when I left off in Chap 3 I had this fanciful notion that Druella would somehow survive. D: As tragic as another loss of life amongst the Blacks is, though, it does an excellent job of propelling the plot and the character development.
I think it says quite a lot about Sirius that, as tense as his relationship is with the rest of the family, he experiences dread at the thought of losing them entirely with no chance to make amends. And as for the death itself, it only heightens the sinister and macabre tone you've already set. It reminds me quite a bit of Agatha Christie's "And Then There Were None." I have the paranoid sense that any member of the family could be picked off next. o.o
"We could all do with a stiff drink or two." Wow, Pollux. What a very Black-esque way of dealing with tragedy.
I love the turn, however subtle, that Sirius and Regulus' relationship takes in this chapter. Despite the tension there has been between them, it's clear that Sirius genuinely cares about his brother's well-being. "It makes the part inside him which winces with every Bludger sent Regulus' way in school Quidditch matches and which let him crawl into his bed when they were younger and Reg had a nightmare twinge with that small stream of guilt which tells him he should have done better." Beautiful. I loved that passage. So well done.
At the same time, that affection is tempered by Sirius' dormant jealousy of his father's affections toward Regulus and of Regulus' attempt to keep his pride around his older brother. I think you've struck a great balance here between affection and resentment.
This line, too, was a gem: "whichever one of them Regulus inherited it from, it's a Black trait nonetheless." Haha. Oh, the glories of the inbred Black family and their cousin marriages. :]
Dude. Where WAS Crouch? Noble stock, indeed. I don't trust that kid as far as I can throw him, and that's not far. -suspicious eyes- Though I don't have any well-formed theory yet, I must say that you've done a great job of continuing to cast suspicion on all multiple parties--Lucius and Crouch Jr. in particular, this chapter. Not only does this keep the plot fresh and interesting, but I have a feeling those red herrings are all going to pan out in the end.
Here is the one theory I do have, and it may be entirely off base, but I think that the house elves know more about what's going on than anyone is giving them credit for. o.- They're the eyes and ears of the household, after all, and I can't help but feel that you've continued to weave them into the story for a reason beyond plot mechanics. But again, that might be totally wrong! :) What's so delicious about this story, though, is that your plot opens the door for plenty of speculation and theorizing--just like a good mystery ought to do.
I thought pacing was excellent in this chapter. You had a huge dramatic incident to center the action around, but you went the extra mile by fleshing it out with emotional development (Sirius/Regulus interaction) and ongoing mysterious behavior. Bellatrix's paranoia in particular continues to reinforce the on-edge ambiance.
Character development continues to go well, though because this was a more action-heavy sequence, I didn't see a ton of growth--and that's perfectly fine, considering this is just one chapter out of several. I will say that I'm beginning to have some difficulty differentiating between Pollux and Orion. I'll continue to keep an eye out for their differences/similarities in the upcoming two chapters.
As to nitty gritties... The narrative contains the sentence "As one, you all glance up at the top of the house," and I wondered if the "you all" is a typo, meant to be "they"? It seemed like an accidental shift from third to second person.
This was, as always, a very enjoyable read. My next reviews may be a few days' in coming, but rest assured I intend to write the next two soon! Fantastic work!