I'm glad I figured this out now, rather than after I'd written the entire thing, because it'll mean I can fix everything from here on in this draft, and only have the first ten chapters to tweak the plot into line when I'm writing the second draft. (Not that I won't be tweaking any plot afterward, but at least this hole will be filled.) What I intend to do is take my outline, rewrite it to adjust for the new development, continue writing from where I am now (mid-way through chapter 11) from the new outline, and adjust the earlier stuff to the new outline on the second draft.
I just hope I don't end up realizing that I need to change a whole bunch more than I realized to make it work. Well, if it turns out changing a bunch more stuff would make the story so much better, that would actually be good. But if that stuff is in the first ten chapters, too, I may end up wanting to start over, and I don't really want to restart the rough draft.
So basically, I really hope I realize that what I'd already planned is quite brilliant with the exception of a few nudges here and there, not a big pile of crap. ;) Wish me luck!