The Mysterious Benedict Society and the Prisoner's Dilemma is the third book in the Mysterious Benedict Society series. The name refers to a social experiment conducted in the beginning of the book.
The book begins with Reynard "Reynie" Muldoon and Constance Contraire. Both are locked in the sweltering third floor of the house of Mr. Benedict.They are playing a game known as "The Prisoner's Dilemma" (as a lesson), but has been adapted by Mr. Benedict to make the game seem real. Instead of prison sentences, Reynie and Constance (and George "Sticky" Washington and Kate Wetherall, the other members) are sentenced to kitchen duty. Reynie is unable to decide which option to choose: both options A and B could make he and Constance do a lot , some, or no kitchen duty, depending on which option Kate and Sticky had chosen.
Suddenly Kate and Sticky arrive through the heating vent. They, per Reynie's instructions, hide behind the door, when the "jailer", Rhonda, comes in, they then lock her inside, much to the fury of Number Two, Rhonda's adopted sister.
Meanwhile, the evil Mr. Curtain is at large and hunting for the Whisperer -- now in Mr. Benedict's possession -- so he can try again to control minds from afar. When a shady businessman shows up with false records that say he's Constance's father, it compels Mr. Benedict to use the Whisperer to uncover her short past. Distraught and confused after all is revealed, Constance runs away, with the whole household after her -- just the distraction Mr. Curtain and his men need to steal the Whisperer and set his evil plans in motion.Of course, the rest of the Mysterious Benedict Society soon find themselves on his trail. They cover their tracks by leaving false clues for the Society, but the Society doesn't notice until too late. In complete accordance with her personality, Kate rushes headlong into Curtain's trap with Reynie, Sticky, and Constance trying to warn her. She ends up getting them all captured. Later, when they're trying to escape, they realize that Kate is the only one who has a chance. Sticky tells her to go, even if only she can get out. But Kate is seen by a Ten Man as she scouted the area. The Ten Men don't hurry as Kate runs to the Salamander. Kate finds out why, McCraken is waiting for her inside. When Kate returns to her friends, she describes what she outside. Sticky and Reynie figure that they were in a real prison that was for demolision. They were on Third Island. They plan another way to escape and come to the idea of using Constance's amazing abilities. Constance sends a message to Mr. Benedict of were they were. After concentrating hard and long, she gets an image in her head. Unsure if it was a dream, for she had fallen asleep because the image had made her relax, or a message, The Mysterious Benedict Society discuss what it meant.