That’s probably harder and more laborious than it sounds. I wrote this article a long, long time ago (September 2007) and our book has changed considerably, but one of the things that stuck with me was how frustratingly difficult it was to break up a bloated chapter. Looking at your case, your process might look something like this.

1) Separate the material by character. If John and Tom and Sue are doing their own things during the 12,000 words, it would probably be easiest to give each of the character separate chapters so that they don’t distract from each other. Readers will be more inclined to ask “wait, what’s Sue doing?” if she made a cameo a few pages ago, which will probably happen if you have one mega-chapter.

2) Add some sort of links between the chapters. If the first chapter focuses on John doing A, you’d have to make us feel that we aren’t totally getting diverted by switching to Tom doing B. Otherwise, it’ll feel like you’ve ended John’s chapter with “TO BE CONTINUED!”

3) Add a cliff-hanger or hook for each separate chapter. Remind readers why they absolutely have to keep reading. Maybe something is at stake, or someone is in danger, the heroes have made a minor discovery that will accelerate their quest, some mystery is shortly about to be solved, or some confrontation is looming, or some interesting situation is staring us in the face. Generally, the key is immediacy. Too many manuscripts (particularly by newer authors) fail because they don’t offer any resolution in the short-term. The characters delve deeper and deeper into an ever-thickening plot that offers far more questions than answers. You might not be prepared to answer the central question of a mystery half-way through (”who’s the killer?) but you can probably give us incremental progress by having the detective pursue and eliminate suspects from consideration. The detective might not know who did it, but he knows one more person who didn’t do it. That’s progress.

In conclusion, I think your storyboard for what used to be the mega-chapter might end up looking something like this. For the purpose of numbering the new chapters, let’s say that the old chapter used to be chapter 20.

CHAPTER 20: John does X, which reveals or causes another problem or mystery.

CHAPTER 21: John does Y to deal with the problem/mystery caused by his actions in the first chapter. There’s some sort of setback.

CHAPTER 22: His attempt to deal with the setback in chapter 2 draws Bruce into the plot. For example, hacker John and hard-boiled private investigator Bruce are investigating the murder of a prominent programmer. John made a minor discovery online that revealed the address of a suspect. It would make sense to have Bruce take the lead in investigating that lead because his skillset and personality are better-suited to the task. Chapter 3 might end with Bruce getting into a fight at the house.

CHAPTER 23: Bruce wins the fight and discovers that there’s more here than meets the eye. The address was a fake, or otherwise a setup. He’s managed to eliminate the lead and he’s probably discovered something about the modus operandi of the criminal(s), but there’s nothing more to learn here. To continue the investigation, he either needs to find another lead somehow or get one from John.

I hope this was helpful. I typically find plotting very difficult.

“Courtney had problems. ^J One, his name was Courtney.”

I immediately met a character, and also realized that the writer had some comic sensibility.

The new version starts with some guy doing some stuff. To me, that’s not as interesting as meeting a sympathetic character.