I have chatted here before about the novel I am writing. I am most of the way through draft 2 with many more in front of me, and I just got to the first sticky point. And to explain my problem it might help to explain how I go about writing a long piece - including the novella I expect to be talking about two weeks from now.
I use what I call the Rising Island Method. You could call it the Sinking Ocean Method, but that sounds gloomier somehow.
So: picture a long mountain range stretching for many miles, but all of it underwater. Got it? Now the mountains start to rise or the ocean starts to sink, as you choose. A few mountain peaks start breaking the surface, forming a few isolated islands. As time goes by more islands appear, and they start to link together, until finally, the entire mountain range is visible.
This is what we in the lit biz call a metaphor. The mountain range is the novel. The highest peaks are the parts I know the most about. Rather than starting at one end and writing straight through I start with the high points (ha ha), because they are the parts I know best (and usually the parts that inspired me to write the darned thing in the first place).
I usually know the first and last chapters very well, but I have no idea how many will fit between them so when I write them I label them Chapters 1 and 1000. That gives me plenty of room to maneuver. Now I know what happens close to midpoint so I write that up and call it Chapter 500. But writing that part teaches me that my hero needs to know something before that point, so I scribble down Chapter 400: Sal finds out X. I'll fill it in later.
And so it goes. Each chapter I write teaches me about other sections I need to write. The islands slowly start to show their shapes.
So why do I find myself in trouble now? Because I have my characters at Point P, and then at Point R, with no explanation of how they got through or around Point Q.
It's not a structural flaw, thank heavens. Just a few chapters that need to be written, and maybe some rearranging. You might call it building a bridge between islands. Or terraforming, if you prefer.
Not to worry. No one will drown in the process. Although a few of the characters do suffer tragic -- well, some other time.