Jeffrey at 2011-09-21 17:41:19:
I can certainly attest to this as well.
My short film, a 15 minute thriller (four characters, one dinner, and one ticking timebomb for dessert, the bomb in this case being the combustible poison all four just ingested...) is still, even at such a short running time, primarily plot heavy. Five minutes of chit chat ("loaded," foreshadow-y chit chit, to be sure) and then the MacGuffin is turned loose from its leash at minute 5. Blood, sweat, and tears take us to fade out.
I know there are a lot of these "contained" thrillers floating around but for my money you still can't do much better than Hitchcock's ROPE for inspiration.