The subplot in a play, movie, or novel is a story that is separate from and less important than the main story.
...a fascinating subplot to the main drama.
subplot in British English
(ˈsʌbˌplɒt)
noun
a subordinate or auxiliary plot in a novel, play, film, etc
subplot in American English
(ˈsʌbˌplɑt)
noun
a secondary plot in a play, novel, etc.
Examples of 'subplot' in a sentence
subplot
There are any number of romantic subplots.
Times, Sunday Times (2012)
But this piece of crime whimsy is all about the wacky hats and the cutesy romantic subplot.
Times, Sunday Times (2010)
The subplots and secondary characters are admirable.
Times, Sunday Times (2016)
As well as this subplot, romantic tales are told by various characters to entertain the hearers.
The Times Literary Supplement (2013)
The game had many subplots.
Times, Sunday Times (2010)
On top of this was precariously piled a series of characters and subplots that looked and sounded like an improvised drama workshop from a citizenship class.
Times, Sunday Times (2007)
The downbeat denouement in the media conference suite had followed some dramatic theatre on Centre Court yesterday with a series of subplots thickening the intrigue.