This is something that I struggle with, and I imagine I’m not alone. That’s why I’m grateful that Danny Manus of No BullScript Consulting answered the following question for Script Magazine: “How many subplots should I have and how do I make them work with the overall story?” Danny responded thus:
A man can’t live on ‘A’ storylines alone – and neither can your scripts. If you’re not crafting and interweaving compelling subplots and B stories into your script, your story will probably feel flat and won’t sustain for 100 minutes.
Your subplots and B stories are what add new dimensions to your script and flesh out your concept and story. Most stories have at least 2 or 3 subplots, and can have more. But you don’t want them to take AWAY from the main storyline, only add to it!
The first 8-10 pages of your second act is where your main character will face their first major test or challenge and take the first step in their arc. But these pages are also where you should begin introducing and developing your subplots and B stories. Somewhere in pgs 30-40ish.
It’s a fuzzy area, but I actually think there are some differences between a B-STORY and a SUBPLOT. I think B stories usually still directly involve your main character, whereas subplots do not – at least not initially.
The B Story is your character’s secondary motivation or mission – the OTHER thing they have to accomplish. Your B Story may be a second problem or issue that your main character has to fix. And while your A-Story presents itself at the inciting incident and is solidified at the end of the first act with the acceptance of the adventure, your B-Story often can’t be identified UNTIL the second act begins, because it’s what is illuminated by the adventure beginning.