It is interesting that Harry's first thought when he enters the headquarters is that it is like entering the house of a dying person. It is not a fullblown foreshadowing, but it is one of those things that in retrospect stand out.

More to the point is Harry's comment that maybe Dumbledore thinks he cannot be trusted. That is true, in a way, but not the way he thinks.

"Guard duty" -- is that really those who follow Harry? Or is this another instance of the Harry is Always Wrong rule? They are guarding the prophecy, aren't they?

The ground is laid (lain?) for the tragedy. Sirius insists on Harry being told what he wants to know, but he is not told enough. Sirius feels (and, perhaps more importantly, makes clear that he feels) trapped and useless. Harry empathises entirely because of his summer so far. These are major plot points. The compromise between Mrs Weasley and Sirius, which means Harry gets some information but not enough, the middle ground is what leads to the tragic outcome. Incomplete information is a staple of tragic plotting (hamartia, I believe (which is often described as a "tragic flaw"), translates as "missing the mark" or some such; and I know George Whalley argued that it was due to ignorance. Of course, Rowling also draws on the more common conception of the tragic flaw as a flaw of personality. Add to that Kreacher's untrustworthiness and Sirius' problematic relationship with him. It is a surprisingly complex plot. I like it.

Oh, and Regulus Black is introduced. We are told he was a death eater and that he backed out and was killed. Sirius' comment that ``I doubt Regulus was ever important enough to be killed by Voldemort in person'' is funny in retrospect.

And the locket is introduced, of course, buried in a list of other strange objects.

The image in Harry's bedroom is also introduced. And Kreacher.