A Subplot Is Not a Rest Stop
A subplot is a second pressure on the story. When it isn’t pressing, it’s a detour with nicer furniture.
You can spot the detour easily. The side romance that never interferes. The relative’s custody battle that resolves itself. The hobby the writer researched for a month. Each is pleasant. Each could be lifted out with two fingers, and the climax would play exactly the same.
A subplot earns its pages by making trouble for the main line. Its complication should spill over at least once and force a decision the plot wouldn’t have faced otherwise.
Say your detective owes a gambling debt. Nice texture, but texture is all it is until the debt pushes him to take a tip from the man who holds the marker, and that tip is what breaks the case open. Now the subplot is load-bearing: the case moves because of the debt, and the reader gets to worry about two things at once.
There’s a pacing dividend, too. Cutting away at the moment of highest tension is the oldest page-turner in the book, and it only works when the reader cares about what’s happening in both places. A subplot that never touches the main story can’t carry that cut.
Economics matter. Every subplot spends attention the plot needs. One good one per novel; two in a long book, if both pay rent.
List your subplots in the margin of your chapter list, one line each. Then trace each thread through the chapters and mark the scene where it touches the main story. Every subplot gets a mark. The one that never touches anything is your next cut, or your next repair.
