In her masterfully crafted murder mysteries, Agatha Christie often layers narratives with disreputable figures, ambiguous motives, red herrings, and escalating tension. Christie’s more streamlined short stories, however, tend to deliver suspense as a precipitous jolt instead of a slow burn. Showcasing the thrills to be had from this concise style, Park Square Theatre is presenting Rule of Thumb, a stage anthology of three one-act whodunits: “The Wasp’s Nest,” “The Rats,” and “The Patient.” With its focus on an adulterous couple locked in a room and framed for murder, “The Rats” offers a morbidly suitable match for armchair sleuths. “The Patient” recounts the ordeal of a woman who believes a near fatal fall from her balcony was not merely an accident. The third work is likely to be a highlight for Christie fans, as it features her master detective, Hercule Poirot, in an early adventure involving an ill-advised love triangle and a thwarted murder.