Jonathan is a school-aged boy living in a futuristic world where there is darkness impenetrable by light outside and in some places inside. The adults can see through it, but all the schoolchildren can't. Adults say it's because of the "Deep Green terrorists" but won't tell them more to the story. At school, Jonathan and his friends Gary, Julie, and Khalid compose the Shudder Club. During recess, the go down a dark corridor into one of the school's "no-go" areas hidden by the strange darkness to initiate Heather, a new candidate for the club. The club had started when Khalid found a scary photo on the school photocopier, a mysterious design painful to look at, and quickly forgotten when not looking at it. The children take turns looking at the picture for as long as they can, and Khalid sets a record of 18 seconds. Jonathan reaches a personal best of 10 seconds, feeling as if he will faint or vomit. In math class that day, a student, Harry (a prospective candidate for the Shudder Club) asks the teacher, Mr. Whitcutt, about "mathwar" and something called "blits" used by terrorists. Mr. Whitcutt explains that BLITs (Berryman Logical Imaging Technique) are images mathematically engineered to stop the human brain. These images are used by terrorists and have killed millions. Khalid asks (unconvincingly nonchalant) if they're all so dangerous, and Mr. Whitcutt says they are. The children continue to believe that their image "doesn't kill people, it makes them stronger." Jonathan wonders what it is about society the Deep Greens don't like and Khalid says it's something about biochips and control systems. Jonathan remembers his parents fighting over biochips. The Shudder Club tries to initiate Harry and he has a seizure. Mr. Whitcutt bursts in and takes the children to the principal's office. The principal decides not to punish them. She says they use that BLIT in their talk with children before they graduate, exposing them for 2 seconds under medical supervision. Mr. Whitcutt says he should've known sooner but is "an old fool who never got used to the idea of the school being a terrorist target." Jonathan wonders why the school would be a terrorist target then blurts out a revelation that the kids all have biochips in their head that make them see the special darkness. The principal says it's to protect them from BLIT attacks and that when they leave school they can control what they see for themselves. That day, leaving school, when the caretaker unlocks the door for the crowd of children and swings it inward, there is a BLIT taped to the outside. The caretaker dies instantly. Jonathan, near the front of the crowd runs and grabs it and crumples it up but sees it first and blacks out. He wakes up in the school sickroom, a hero for saving all the children. Mr. Whitcutt says everyone is shocked he survived and is sane, and realizes it's because the children in the Shudder Club have built a level of immunity to BLITs. Mr. Whitcutt says this will change everything, that the biochips will be reassessed and perhaps discarded in favor of a system of immunization through exposure. As a present to Jonathan, they have turned off the darkness so that he can see out the window and see the sunset, and his friends send him a chocolate bar with a note that says, "That which does not kill us, makes us stronger."