The main plot of a screenplay, the A story, is usually about what the protagonist wants: catch the killer, win the race, pull off the heist. Subplots are the other threads running alongside it. Done well, they give a movie depth, rhythm, and emotional weight. Done poorly, they're detours the audience tolerates while waiting to get back to the real story.
What subplots are for
A subplot earns its place by doing something the main plot can't. The most common jobs:
Carrying the theme. The A story is often external and active. The B story frequently carries the film's emotional argument: the relationship through which the protagonist learns what they need to learn.
Driving character change. Many films route the protagonist's arc through a secondary relationship. The hero wins the external fight in the A story, but the reason they're able to win is something they learned in the B story.
Varying rhythm. A relentless main plot can exhaust an audience. Subplots provide changes in tone and pace, a quiet scene after a loud one, without stopping the story.
Complicating the main plot. The best subplots collide with the A story, creating obstacles or raising stakes at crucial moments.
The B story
Many screenwriting teachers single out one subplot as the B story: usually a relationship, often introduced around the end of the first act, that becomes the emotional heart of the film. In a romance it might be the friendship that teaches the heroine to trust. In a thriller it might be a strained marriage that the case puts under pressure.
The B story often provides the key to the climax. When the protagonist hits the low point near the end of Act Two, it's frequently a realization from the B story that gives them the insight or strength to go on.
How many subplots?
A feature can typically hold one strong B story and two or three smaller subplots. Ensemble films hold more, but every additional thread takes screen time from the others. If a subplot has only a few scenes and doesn't affect the ending, consider whether it's earning its pages. Our guide to scene counts shows how quickly a feature's scene budget gets spent.
Each subplot needs its own shape
A subplot is a story, which means it needs a beginning, a middle with complications, and an ending. Threads that are introduced and then simply stop feel unfinished. Before drafting, write each subplot as its own short outline: how it starts, how it develops, how it resolves, and where in the main plot each of those beats lands.
Weaving them together
The craft of subplots is mostly in placement. A few principles:
Connect them causally. The strongest subplots affect the A story. A betrayal in the B story creates an obstacle in the main plot. A decision in the main plot damages a relationship. Threads that never touch feel like two movies.
Resolve them near the climax. The most satisfying structure lets subplots resolve close to, or as part of, the main climax. The emotional payoff and the plot payoff land together.
Rotate, but don't abandon. If a subplot disappears for thirty pages, the audience forgets it. Return to it regularly, even briefly.
Let them comment on each other. When the B story explores the same question as the A story from a different angle, the film starts to feel unified. This is often how theme becomes felt rather than stated.
Common problems
- The subplot belongs to a different movie. It's interesting on its own but has nothing to do with the protagonist's journey. Cut it or connect it.
- Too many threads. Each one gets too little time to matter. Merge characters, or cut the weakest thread.
- No resolution. A subplot that's dropped without payoff reads as an oversight.
- The B story overshadows the A. If the secondary story is more compelling, consider whether it should be the main plot.
A planning trick
Use a different color or symbol for each subplot when you outline. On index cards, a colored dot in the corner shows instantly whether a thread vanishes for half the script or crowds out the main plot. Many writers find imbalances in minutes this way that would take a full read to notice.
In a draft, a quick read of your scene list can do the same job. In Quillit, the outline shows every scene in order; mentally tag each with its thread, and gaps become obvious.
Subplots make the main plot matter
The deepest function of a subplot is to show what the main plot costs. When the external mission puts real relationships at risk, every choice the protagonist makes carries weight beyond the plot. That's when a story stops being a series of events and becomes about something.
