Rather than subordinating one plot to other – that is, rather than make one a subplot – why not treat them with equal importance? When two dramatic plots occur at the same time in a story, usually involving different characters but the same theme, you are employing a parallel plot structure.

A novel with such a structure might involve two main characters who each face a different problem to overcome. As they close on solving their individual problems, those efforts bring them toward one another, and their problems increasingly entwine, though they may remain unaware of one another.

There are many variations of parallel plot structures, though they typically involve “two” or more characters. For example, suppose your science fiction story is about an author whose memory of his past life has been wiped clean. As going about his life, he pens a novel about a character who the reader realizes actually is about the author’s life before losing his memory. The “two” characters are the author writing the story and the protagonist of his manuscript – that is the author before and after losing his memory.

Parallel plot structures often appear in science fiction, literary fiction and metafiction. That’s because this technique lends itself to complex explorations of reality and ethical principles, both of which are common themes in those genres.

Despite the great variety and creativity this structure allows for, there are a couple of basic guidelines that should be followed to make the manuscript work:
• Each plot must be able to stand on its own. The author really is writing two (or more) books as both (or all) of the main characters must face conflict as they solve some overarching problem that sets their stories in motion.
• Each plot ought to have some theme or motif that ties them together. The story’s two plots can be set in different eras or locations or one even can be “fiction” while the other is “real.” What connects them is some concept or message (e.g. truth, love, loyalty, etc.) that is explored through two different experiences. Sometimes authors use this plot structure to thematically show that one path is better (or even no better) than the other.
• Each character, if brought together in the plot, should have a logical reason for this meeting to occur. Their meeting or passing must be believable, arising out of their separate stories. If not, the meeting will feel contrived.