The is not a reliable source
The children quickly decide that they will follow the clues and go to Mr. Benedict's aid in secret. Rhonda reveals that Mr. Benedict gave her a letter before he was kidnapped, and told her to open it when the other children arrived. The envelope contains a message of greeting from Mr. Benedict, and a nonsensical riddle. In solving the riddle, they discover that the words are in alphabetical order. This leads them to a dictionary, and then a journal - in which is another nonsensical riddle. The children discern it to mean TAKE THE SHORTCUT. The children sneak off on the The Shortcut, the “fastest ship in the world” and find more information that takes them to a castle in Portugal. The Shortcut is the new cargo ship captained by Mr. Benedict's old Navy friend, Phil Noland. Within a few days they land in Portugal, where the children are dismayed to find that Ten Men are stationed on the journey's trail to catch them. At the destination of the next clue a couple Ten Men catchff long enough for Milligan to suddenly arrive (his first appearance thus far) and whisk them away to safety. He accompanies them to a remote island in the middle of the ocean where Mr. Curtain has Mr. Benedict and Number Two held.
From there, hidden evidence directs them to a library in Thernbaakagen. There they learn that the “mysterious plant” is called duskwort and is extremely rare - possibly extinct. It has the power, when burned in fire, to put entire villages to sleep for hours on end. It also is a possible antidote to Mr. Benedict’s narcolepsy (Mr. Benedict found this out because of his parents and his parent's great friend). Researching the duskwort, they find that no one knows what it looks like. They travel to a hotel, but are found by two of Mr. Curtain’s henchmen, called the Ten Men. However, they are rescued by Milligan, who accompanies them to find more evidence. They finally find the location of the duskwort - an abandoned island.
At night they keep watch at the top of the silo in the middle of the village, and Number Two is revealed to have escaped. However, she is malnourished and injured, and cannot give much information as to what's going on. After getting captured by Ten Men and making an escape, the children get to the mountain cave where Mr. Curtain is stationed. They discover Mr. Benedict chained to the wall in a cave. He begs them to destroy the duskwort. Upon the children saying they don’t know what it looks like, he jumps up and reveals himself to be Mr. Curtain, and locks the children to the wall with the real Mr. Benedict. Mr. Curtain leaves after Mr. Benedict tells him where the duskwort is. However, McCraken then appears to report that Milligan jumped off a cliff to avoid capture. Kate bursts into tears, and when Mr. Benedict tries to comfort her he falls asleep in his grief.
Later, when the children are left alone, Kate is optimistic as usual and tells her friends that Milligan would never have jumped to his death - not if they were still in danger. So when Mr. Benedict hypnotizes S.Q. Pedalian into unlocking their handcuffs, they get away. They make their way to the edge of the island and discover Milligan, who is terribly injured but had been trying to crawl back to save them. He says he'd been to that cliff before and saw the bottom was all mud and about a 50 foot drop. He sheepishly admits he'd made a slight misjudgement in the darkness and ended up hurting himself.
Against his wishes they bring him with them, and when they get to the beach Captain Noland grounds his ship to distract Curtain and the Ten Men. All the passengers and our heroes hide in the hold at the bottom of the ship to protect themselves from the villains. When their location is discovered Constance cries out that they've set an explosive to dislodge the door just as the Coast Guard arrives. Kate takes the explosive and almost throws it at Mr. Curtain, who's on the shore, but instead throws it into the ocean, reasoning that to kill them would bring her as low as them. Mr. Curtain therefore goes uncaptured and escapes, but everyone is safe and sound. When they return home Mr. Benedict insists that they all stay at his home to ensure everyone's safety.
Reynard "Reynie" Muldoon is a twelve-year-old living with his wonderful tutor, Miss Perumal, who is teaching him Tamil. Exceptionally bright, Reynie looks between the lines, observing and questioning, and gets past most obstacles by finding the "puzzle" within the situation. Reynie is an especially average-looking boy with average brown hair, average pale complexion, average clothes, and average height. He is sort of like a leader to the rest of the Mysterious Benedict Society.
George "Sticky" Washington is also a twelve-year-old boy. He is characterized by his intelligence and ability to remember everything he reads—hence his nickname, for everything sticks in his mind. He strongly prefers this nickname to his given name, George Washington. Sticky ran away from his home after feeling that he is not wanted by his parents, but is now living in is home with his parents again. He has tea-colored skin and is bald because he used hair remover to disguise himself. Sticky also has a bad habit of polishing his spectacles whenever he gets nervous. Sticky also ran away because his brain needed a rest from contests that his parents entered him in for his intelligence. His family spent a fortune finding Sticky, leaving them very poor. In this book Sticky is becoming more comfortable with his gifts.
Kate Wetherall is an energetic thirteen-year-old girl who became an orphan as a young child when her mother died and her father left her. She found out that Mr. Benedict’s spy, Milligan, is her father, and was separated from her by force. She now lives with him on a farm. Kate finds any and all shortcuts in a conflict, and carries a red metal bucket which houses a great many things which she uses to overcome obstacles and evade capture. She is very physically capable and almost fearless, often rushing into things without giving them a second thought. She is very optimistic and always tries to make the best of a situation. She is also very brave, especially when it comes to helping her friends. She has long, golden-blonde hair, nearly always tied back in a ponytail, and ocean-blue eyes.
Constance Contraire is the fourth child of the group. Though she at first does not appear to have any special abilities, her bravery and stubbornness ultimately prove to be a great asset. Constance can detect patterns in things, and though it may seem like she is psychic, Constance merely recognized patterns and unknowingly can predict the near future. She has wispy, light blonde hair and pale blue eyes. Constance is only three years old which explains her frequent napping and obstinacy.
Mr. Benedict is a little older then middle-age man who recruits the children that later call themselves the Mysterious Benedict Society. He is the one who discovered the plans of his twin brother, Ledroptha Curtain. However, none of his colleagues believed him and called him crazy. Mr. Benedict suffers from narcolepsy, which causes him to fall asleep when experiencing strong emotions (usually laughter).
Mr. Curtain is Mr. Benedict's evil twin brother, who has kidnapped Mr. Benedict and Number Two in the attempt of taking over the world. He wears silver glasses and green plaid suits, and usually makes his way around in a motorized wheelchair. Like his brother, he suffers from narcolepsy, but his condition is triggered by anger as opposed to laughter.
Rhonda Kazembe is Mr. Benedict's adopted daughter. She comes from a country in Africa. She is also, like Number Two (shown below) an assistant to Mr. Benedict, though she does sleep. She is quite beautiful, with very dark skin and coal-black hair. She has a very good memory.
Number Two is Mr. Benedict's assistant and adopted daughter. She almost never sleeps, and takes sudden food breaks to keep her energy up. Her real name is not mentioned in this book, as she prefers to use her code name. She has rusty red hair, a yellowish complexion, and always wears yellow.
Milligan was a spy captured by Mr. Curtain. Though his memories were erased by Mr. Curtain, he managed to escape and eventually became Mr. Benedict's bodyguard. However, when the four children are in danger and he desperately needs to save them, that triggers his memory and is revealed to be Kate's father. By the second book many of his physical abilities as a secret agent have been revealed, including being able to devise a lockpick from nail clippings, being able to bend metal bars, and being able to expertly handle his signature tranquilizer gun. He has blonde hair and ocean blue eyes like Kate.
In a starred review, School Library Journal described the book as "not just a rip-roaring adventure ... but also a warm and satisfying tale about friendship." Kirkus Reviews was less positive, saying that the book "may wear down less patient readers", citing the prose and needless elaborations in several areas. Horn Book Magazine disagreed, saying that "Stewart keeps interest high throughout". They especially praised the "first-rate brainteasers", with School Library Journal also commenting that it had "plenty of clever twists".
The beginning of the novel came in for particular criticism, with Horn Book Magazine complaining of "a few treacly initial scenes" and School Library Journal saying that "[t]he action takes a while to get going". However, comparing it overall to its predecessor, Horn Book Magazine felt that it was "a worthy successor" - although Kirkus Reviews said that it "has more of an air of trading on the previous one's cleverness than building on it."
A sequel for this book (and a third book in the series) was published October 6, 2009. The title is The Mysterious Benedict Society and the Prisoner's Dilemma, according to the Little Brown and Company Spring-Fall 2009 Rights Guide.