Hi DD! I'm about mid-way through the most complex writing project I've ever done (several stories with some red thread storylines progressing in the background, so a sort of interwoven structure). I have an outline of the major plot beats, but the problem is, I've gotten about 2/3 of the way through, and this is where I've started to have trouble bringing my many threads together. The further I go, the the harder keeping it all clear and elegant becomes. Any advice for working at this stage?
It may seem counterintuitive, but once I'd found myself in a situation like this, I would immediately start working backwards.
It's difficult to describe what I mean here except semi-graphically—sort of in terms of one of those strings-pinned-to-the-wall diagrams so familiar to a lot of us from the various evidence-wall memes.
If we're imagining your present as-yet-unconnected threads as more or less progressing left to right, I would "stick pins in them" at their current furthest range and then move straight out to the far right side of the diagram.
For each thread I would then get busy establishing a detailed "end state" for the work: meaning a sense of what you want each of those through-line of plot to look like when you're done in terms of characters, situations, etc. I'd make very sure that all the major through-lines were covered, and (in passing) take a long look at how they'll stand in relationship to one another when all the action's finished.
Then I would start working back along each line toward the center of the matrix—looking to see what the next-to-last thing was that needed to happen to produce the final result on a given through-line. And then the third-to-last. ...And so forth.
I would try to work through the whole set of through-lines for each given step or stage before progressing any further backwards—unless, of course, some leap of logic occurs that makes an obvious connection between two different through-lines, or an earlier stage in the same TL that hadn't been obvious before.
(Is this making sense? God, I hope so.)
My experience with this kind of situation in the past is that it doesn't take too long before, on one or two of the lines you're constructing backwards, you'll hit something fairly major that somehow hadn't come up for consideration previously, or had simply slipped or fallen off the structural "radar" because so much other stuff had been going on around it. That event or piece of data, once perceived, will very often either immediately connect itself back to one or more of the "pinned" through-lines, or promote one of the other incomplete ones into growing connections to other adjacent lines of plot material. It's a little like watching neural tissue developing alternate pathways for itself after an injury.
...Anyway, give this approach a shot and see how it works for you. There are times when simply the act of reversing direction on the plot build will shake something loose in the business surrounding the building-it-forward part. It's worth a try to see what happens.
Hope this helps!