The other day I sat through a film featuring a subplot that had nothing whatever to do with the main thrust of the film. It didn’t reveal anything about the characters or the storyline, it didn’t hint at motivation, it wasn’t even a credible red herring. Completely irrelevant. I can’t even remember the title. However, it had an unexpected, but very useful consequence.

After the successful conclusion of an important subplot of my own, in which my mother in law was transferred to residential care when her dementia became too advanced to manage at home, I found myself with an unaccustomed amount of free writing time and not a word in my head. Tum-te-tumming at the keyboard I recalled the film with the inconsequential subplot and looked at it through the lens of my own perspective. What purpose should subplots serve in novels?

Long-term caring for a relative was a voyage of discovery.  It informed all aspects of decision making, delivered tension and suspense, revealed character traits. It added interest and complexity to my personal story and temporarily changed its trajectory. In short, the whole caring experience was a subplot to my life.

Likewise, in fiction, subplots should add value to the story. They could complicate your characters’ lives and stir them up a bit, make things more interesting, pose questions and present difficulties. They can interrupt proceedings, slowing down a hurried storyline and introduce clues to support the main narrative. They can move independently, beside the main story, or be interwoven within it.

How you do it depends on your skill at handling several strands at the same time, like knitting a Fair Isle sweater. Some patterns and colours are in play all the time, others only make an occasional appearance, but they all help to create a colourful and satisfying whole.

Here are a few suggestions on how to make subplots work for you:

• Change the pace by interrupting the narrative flow, adding texture to an otherwise linear story.
• Create contrast between characters and situations.
• Change mood by injecting humour, menace, intrigue.
• Create suspense and curiosity.
• Offer explanations and resolutions.
• Build expectations.
• Reveal information.
• Enhance understanding.
• Connect characters in unusual or unexpected ways.
• Develop relationships outside the main thrust of the story.
• Introduce a story within a story.
• Provide red herrings to distract attention.
• Add interest to a saggy middle.
• Present the opportunity to switch viewpoints.
• Provide a mentor character.

In the first half of my novel, Breaking News, my heroine, Sara, interviews a male character for a news item. His story is dealt with over a couple of chapters but the thread is carried along in the background until he appears again, much later, to upset a seemingly satisfying conclusion. I wanted to show Sara’s strength and resilience, but I didn’t want a coincidence or a stage-managed situation that wouldn’t ring true to the reader. By introducing him early on, and apparently wrapping up his problem, he could recede into the background until I needed him again. Unlike the subplot in the film, he wasn’t an extraneous sidebar; he had a purpose.

Subplots can be as large or as small as you need them to be to serve your story. They can start at the same time as the main plot, or be introduced when you need some added texture. They can run alongside each other or be interlinked. If they heighten anticipation by offering twists and tensions they will bring a satisfying complexity to the story that will undoubtedly please your readers.