Runaway Jury sets up as a battle royal between Dustin Hoffman’s Wendall Rohr and Gene Hackman’s Rankin Fitch, with Fitch the powerful opponent. Most writers would work their plot from there, using the hidden powers of the main opponent to provide most of the surprise upon which plot is based.
But Grisham adds another element that magnifies his plot tremendously. John Cusack’s Nick Easter seems to be the innocent little guy who will, in classic thriller form, come under intense attack from the powerful opponent. But instead of using the reactive victim, Grisham gives Easter his own desire line, his own hidden agenda. The result: three sources of action and massive plot (see the Great Screenwriting Class for details on plotting, opposition, surprise, the reveals sequence and plot weave).