One of the most common plot problems writers face is mistaking minor characters and subplots for the main character and primary plot. In the following excerpt, Joseph Bates, author of The Nighttime Novelist, discusses overactive or inactive characters and subplots and how they can impact your story.
Overactive or Inactive Supporting Characters
If in the second act you find your novel veering off course either because a minor character has come in and tried to run the place, or because your minor characters seem to be doing nothing but sitting on your couch, eating your food, not really contributing, you should put them to the test: determine why they’re there, if they can be brought in line somehow, or, if not, how you might excise them from the novel.
Minor characters who become personal “darlings” for the author can be very hard to kill, and often a writer will find some way to justify keeping around an inactive but favorite minor character based on very thin reasoning, such as saying that the character adds comic relief (yes, but comic relief to your depressing post-apocalyptic Gothic revenge story?) or that the character adds a romantic element (yes, but does your chainsaw-murderer bipolar anti-hero really need a love interest?) or, or …
If an inactive supporting character does indeed seem to fulfill some function like this—but is otherwise inert—you might see if another and better-established supporting character might fulfill that role just as easily. Or you might consider streamlining several supporting characters into just one who does the trick.
Ultimately what stays and goes is not up to you as the author but up to your story. When in doubt, try to listen to what the story is telling you to do and follow that advice; it’s almost always going to be right. As for overactive secondary characters—those who seem intent on making their story the novel’s big one—see the section on overactive or inactive subplots [below] for tips on getting them under control.
Overactive or Inactive Subplots
Subplots exist to tell us something about your protagonist and his quest. They’re like a side mirror, offering a quick, new (and helpful) perspective and allowing the readers to keep moving forward unimpeded. Thus a subplot becomes problematic when that function breaks down, when it becomes either overactive—trying to take over the main plot and tell its own story instead—or inactive, meaning that it has no clear, compelling connection to the protagonist and the main arc; it’s simply there.
An overactive subplot behaves almost like a virus. Its ultimate goal is that it wants to live, like everything else on earth, but in order to do this it invades something healthy–your main plot–and tries to take it over. It might be that the subplot is auditioning for its own novel—it isn’t unheard of that a subplot becomes so alive that the author eventually decides to tell that story on its own—but it can’t be allowed to take over this one (unless, of course, you come to the realization that the subplot is the plot you actually wanted to explore all along, in which case, well, it’s back to the drawing board).
An inactive subplot isn’t nearly as aggressive; it’s not doing anything to take over your novel, or much to advance it, either. In fact it’s not doing much except taking up pages and keeping the reader from following the main arc. Most times an inactive subplot exists because the author likes the character of the subplot and has a soft spot for it (even though she probably realizes that there’s no reason at all for the subplot to exist). You should ask yourself what the subplot might do in the story, why you included it to begin with. If the subplot could have some bearing on the character or main arc, then it might be rehabilitated, making it clear what that relationship is. But if you come to the conclusion that it doesn’t really have a bearing on the main action, you have two options: “absorb” it into a preexisting subplot, one that does have a reason to be there, or get rid of the subplot altogether.
Again, your subplots are there to further the reader’s understanding of the main plot, character, and conflict. But if the relationship between plot and subplot becomes imbalanced, you’ve got to reestablish the relationship or excise the subplot, as the direction (and fate) of your novel is at stake.