with the actual plot
leading the story of the film there can also be a subplot
(or more) supporting the
themes of the film. A subplot enriches the film.
example: In the film "Rio Bravo" the main plot is
about the sheriff (John Wayne) fighting against the gang lead
by Burdette, who tries to free a prisoner charged with murder.
The subplot is about the sheriff's friend fighting to stop
Hawks: Rio Bravo 1959. [us.imdb.com/Title?0053221]