Longman Dictionary of Contemporary English
story line
noun
EXAMPLES FROM CORPUS
▪ I think it has a great story line, I hate Carmel!
▪ It can make a story line clearer, which is always an advantage.
▪ Trust remains the central story line.
▪ You do not have to stick to the story line.
Wiktionary
story line
n. (alternative form of storyline English)
Usage examples of "story line".
In fact, only those already immersed in Jordan's universe will be able to follow the multitude of characters moving in and out of the story line, each one picking up a thread, advancing it, and dropping it, perhaps to return to it later in this book, or, perhaps, in the next.
The good reader asks what the work means besides its obvious story line.
If such additional details are really necessary for the story line itself, it would be better to provide another dose later on, after allowing time for the first to sink in.