Mid-chapter 20
Must do this because I figure that the fact that Luna's not down at the river and that Mr. Lovegood just sold them out will be revealed at the end of the chapter for the chapter-cliffhanger.
So. The Hallows. We know Grindelwald had the wand that he got from Gregorovitch. Potter has the cloak. Could the stone be the Philosopher's Stone? If so--and if Dumbledore didn't lie when he said he destroyed the stone..that'd be a nice way to tie it to the first book. And the stone's probably in Hogwarts.
The wand...I dunno where it would be, since I imagine Grindlewald wasn't imprisoned with his wand.
At any rate, I think it won't be assembled--after all, Rowling is big on how death is something you not only can't escape, but shouldn't attempt to. Or if it /is/ assembled, it'll have to be destroyed.
....Oh. Two + Two = Four. Dumbledore was helping Grindelwald as a kid because Grindelwald had told him about this and he wanted to make the thing to save his sister, who was really, honestly ill. Then Aberforth broke Dumbledore's nose because he knew if he hadn't rejected Grindelwald--or whatever happened--he would've been able to save his sister.
There. That is both plausible, and fits with all the info. Dumbledore was just desperate to get info out of Grindelwald to save his sister.