And as always, actually writing something proves to be the antidote to not writing anything. I did like I suggested I might do: I skipped a bit ahead from the scene that was giving me troubles, and without much difficulty churned out a few more lead-in scenes to the Halloween chapter.
Clearly there's something wrong with that scene I was having problems with. Maybe it's a scene that shouldn't exist at all, or maybe I'm just going at it the wrong way. I hope it's the latter, since the scene foreshadows something that happens to two of Samantha's friends. It's not a thing all that important to the plot, but it's interesting and fun, and I want to do it, so I'm going to keep trying.
But in the meantime, it seems to be all clear for now. I didn't wrote a lot, but what I did write came very easily, and I could feel many more words happily waiting their turn as I sat at my desk yesterday afternoon. That's how it's supposed to be; and fortunately that's how it's been lately, more often than not. That's only the second time I've been really stuck like that. The rest of the time it's been relatively smooth sailing.