Act three brings all your characters, their roles, and relationships to a climax. Previously, you described how your characters arrive at that climax. Now, we need to get a bit more precise about exactly how you will unfold these crucial moments - the order in which they will happen within the third act.
One might think that a climax is just the moment at which something is ultimately resolved. But in stories, it’s more like a cascade.
By the end of act two, you have locked your characters into structural, situational, and emotional relationships that have set in place, like raisins in rice pudding. Being an act of growth, things jockeyed around a bit, while the pudding thickened, until they finally appear to be fixed in a strained position.
But, there is more than meets the eye. These relationships are not set, but merely stuck. Each is like a wound-up spring held by a latch, the tension building along fault-lines before an earthquake, or the floor filled with mousetraps in the movie "Mouse Hunt."
All it takes is one little trigger that springs just one of the relationships, and a domino-like cascade begins until all the relationships are sprung.
Think of it as a chain reaction. Something upsets one uneasy truce, and the resultant energy snaps two more into upheaval. They affect four more, then sixteen, and before you know it, the whole lot of them is thrashing about, almost chaotically.
What's more, just because one relationship snaps, doesn't mean it is done changing. In fact, the other snapping relationships around it tend to wind its spring all over again. So that by the end of the third act, every relationship has sprung into a new form, then built up a whole new kind of tension and is ready to spring again.
That is when final climax where it all goes up at once, like a fireworks show, and the character relationship tension is finally spent.
What triggers the first spring to snap? The plot. There will be some event, often apparently innocuous, that upsets one of the stable but tense relationships, and ultimately triggers the whole cascade.
Now keep in mind that everyone doesn't have to shift 180 degrees. Nor, do your characters have to be at high- intensity all the time. Rather, explore the moments of the springs tightening and loosening as other relationships alter under the strain.
The main things to remember are that the overall tension among characters should build over the course of the third act, and that the beginning of the third act should show how locked up potentials established by the end of act two now begin to rattle and unwind.
In this step, then, develop and describe the specific instances in which roles and relationships begin to vibrate and rearrange themselves, adding to the overall tension of your novel in the beginning of act three.