A throughline is that invisible glue that binds your story together. It is like a thread that ties your narration together to form a story and keep it on track. It refers to the critical elements of your story that must be kept consistent throughout the narration if the story is to have good flow and consistency. Your throughline is the driving force of the book that keeps the story going and the reader captivated. It is possible for your story to have more than one throughline, but there is always the pivotal one around which the entire story is centered.

The concept of a throughline may be explained differently by different people. In Hollywood, for example, screenwriters may describe a throughline as the unwavering force that keeps the story going, makes it captivating and brings the pivotal character to life. Other writers may describe it as the embodiment of the protagonist's conscious desire - something that reveals that the main character knows what they want and they are aware that they want it. It can also be described as the desire, shared by readers, that creates a forward momentum, makes the story captivating and shapes the narrative.

For example, at a certain point in the story, often somewhere in the middle or close, the pivotal character is denied what they want, either by the power of outside circumstances or by their own choice. This moment gives a deeper motivation for the story to go forward. The force that compels the main character to go on becomes a sort of throughline on its own - a secondary one. The throughline keeps your main character on track and, by doing this, helps the writer keep the whole plot in line. Whatever subplots you come up with, the throughline acts as the guiding light that keeps you in line so you do not lose sight of your main goal for the story. By propelling your protagonist forward and keeping them on track, the throughline also defines the overall momentum of the story.

There is also what is called the overall story throughline, and this is one that brings all the characters together and does not just focus on the pivotal character. Such a throughline sets the backgrounds against which the author tells their story and has significant influence throughout the narration.

Although your throughline must remain consistent throughout the book, this does not mean that it should stay static. Allow your throughline to evolve with the story. As your story takes shape, the characters grow and this should reflect in the throughline. An evolving throughline mainly means developing secondary throughlines while keeping the primary one consistent. Irrespective of any changes that may occur along the way, the main throughline, the one that drives your main character, must remain the same. This way, the reader never questions what is driving the story.

Remember, your story is allowed to have more than one throughline. In fact, it will almost certainly have multiple throughlines, but there is always the main one that ties everything else together. All these throughlines keep your story moving and the characters on track. They guide the character's actions and emotions.