Definition of "underplot"

underplot

noun
plural underplots
1. A subplot; a plot that is not the main plot of a story.
  Quotations
  I have not been able to discover the source of the very curious underplot of The Captives.
  1882-89, A Collection Of Old English Plays, Vol. IV‎
  Thus, again to quote Mr. Homer Smith, it has been held that 'In general the pastoral incidents serve as an underplot, utterly foreign in spirit to the main plot.'
  1906, Walter W. Greg, Pastoral Poetry and Pastoral Drama‎
2. A secret scheme or trick.