Plot
The story of Wool takes place on a post-apocalyptic Earth. [9] Humanity clings to survival in the Silo, a self-sustaining subterranean city with 144 floors. No records of the time before the Silo remain. All residents of the Silo are taught that the outside world is toxic and deadly, and the Silo's cardinal rule is that anyone who expresses a desire to go outside must be sent there to clean the external sensors with a wool cloth. Those sent outdoors invariably clean the sensors as instructed, but die within minutes, reaffirming to the Silo residents that the outside is uninhabitable.
Wool
Wool is the first act of the series, and consists of books 1 through 5: Holston, Proper Gauge, Casting Off, The Unraveling, and The Stranded.
Holston is the sheriff of the Silo. Three years ago, Holston's wife Allison became convinced that the outside world was livable and that the IT department, which runs the external sensors, had deceived the rest of the Silo. She went to clean willingly, but apparently perished. Still grieving the loss of his wife, Holston also asks to go outside. He is given a protective suit and sent outside, but when he exits the Silo, he sees a healthy, vibrant world. Encouraged by this sight, he happily cleans the Silo's external sensors and then explores the environment. However, he is forced to remove his helmet when he runs out of air, and at that point, he discovers that the world is actually toxic and his wife truly is dead. The suit's visor had been masking reality with a computer-generated image. Holston dies near his wife's abandoned body.
Following Holston's death, Mayor Jahns and Deputy Marnes embark on a trip to the Mechanical zone, the Silo's lowest level, to interview Juliette Nichols, their top candidate for sheriff. Along the way, they visit the IT department. Bernard, the head of IT, demands his own preferred candidate for sheriff, but Jahns is dismissive. Later, Jahns is impressed by Juliette, who quickly proves herself to be responsible, stubborn, and independent. Juliette agrees to become sheriff on the condition that she is permitted to perform long-overdue mechanical maintenance, which requires a power blackout, and Jahns assents to the plan. Bernard is incensed by the blackout and Juliette's appointment, and poisons Marnes's canteen on their way back up, resulting in Jahns's death.
Bernard is elevated to mayor and eventually replaces Juliette with his own choice for sheriff, Peter Billings. He also trains a man named Lukas to become his successor, and teaches him the secrets of IT: the IT department is the true power in the Silo, and records of knowledge from the old world have not been lost, but confiscated and sealed in a hidden chamber. However, Peter's honesty and pursuit of justice makes him difficult for Bernard to control, and Lukas has no interest in perpetuating Bernard's agenda. Bernard finally finds a pretext to condemn Juliette to a cleaning, but one of Juliette's friends in Mechanical, Walker, secretly arranges for her protective suit to be made out of quality materials, unlike all previous protective suits which were secretly designed to fail and constructed of intentionally defective materials. When she exits the Silo, Juliette realizes that her suit's visor contains a high-resolution display, and is deceiving her. Instead of cleaning the sensor, she becomes the first cleaner to walk out of the sensor's range of sight.
Juliette finds the entrance to another Silo. Inside, she encounters a middle-aged man called Solo who explains that this is Silo 17 and he is the last survivor of an uprising decades ago. Solo reveals that there are dozens more Silos, and he shows Juliette how to communicate with them, including her own Silo 18. Juliette makes contact with Lukas and they develop a relationship. He also tells her about IT's secrets, and relates that after she left, Silo 18's Mechanical staff launched a rebellion against Bernard. When Bernard decides to send Lukas to clean, Peter has Bernard placed in the airlock instead and demands he defend his actions. While arguing with Juliette via radio, Bernard reveals his driving purpose was to protect Silo 18. Silos are frequently disrupted by rebellions, but most are put down; when a rebellion is successful, the Silos' managing authority in Silo 1 will exterminate that Silo's inhabitants. Bernard only wanted to maintain order in Silo 18 and prevent any rebellions from breaking out. However, Peter judges that in working toward that aim, Bernard committed crimes against the Silo, and sends him out to clean. Juliette thinks Lukas is being sent out and tries to save the person released into the air lock, which is actually Bernard. Bernard refuses to go outside or be saved by Juliette and dies in the airlock during the cleansing fire. Lukas assumes control of IT. Juliette, while recovering from her burns, is elected as Silo 18's next mayor by a grateful populace.
Shift
Shift is the second arc of the series, and consists of books 6 through 8: Legacy, Order, and Pact. It is a prequel to the Wool arc.
In 2049, freshman Congressman Donald Keene is recruited by Senator Paul Thurman for the CAD-FAC (Containment and Disposal Facility) project, ostensibly an underground repository for the world's nuclear waste to be constructed in Fulton County, Georgia. Donald, who has an education in architecture, is tasked with designing a self-sustaining shelter, a Silo, that will be built near the CAD-FAC for facility workers to use during emergencies.
In 2052, the CAD-FAC is completed and the site above it hosts the Democratic National Convention. Donald and Thurman are present for the opening ceremonies when a nuclear blast destroys Atlanta, and they and other attendees are ushered into the CAD-FAC. Thurman reveals that CAD-FAC was a cover for World Order Operation Fifty (W.O.O.L. [a] ), an initiative to preserve humanity in the event the species was threatened with extinction. Nuclear detonations have scourged the Earth's surface, and it will not be safe to resettle it for 500 years.
The shelter consists of 50 total Silos. They are managed by Silo 1, which houses Operation Fifty co-leaders Thurman, Erskine, and Victor, and other key personnel such as Donald. While 49 Silos have generational populations, Silo 1's inhabitants are cycled in and out of cryogenic stasis every few decades to work six-month shifts guiding Operation Fifty through the centuries. The other Silos suffer internal rebellions of varying intensity every couple of decades. Major rebellions are treated with "resetting": the population is reduced, the remaining residents are given amnesia-inducing medication, and the computers are wiped. When a rebellion overtakes a Silo completely, overwhelming its IT department or gaining control of the airlock, Silo 1 terminates it by remotely activating poison gas.
By 2212, Operation Fifty has entered a crisis. A cluster of eleven Silos, led by Silo 40, severed contact with Silo 1 and jammed the termination signal, forcing Silo 1 to resort to demolishing them. On the heels of that, a rebellion begins in Silo 18, and concerns mount that the entire project is doomed to fail. Donald is awakened on Thurman's orders to find a solution after Victor, the mastermind behind Operation Fifty, commits suicide. Thurman and Erskine divulge to Donald that they headed a conspiracy that instigated the nuclear apocalypse, and justify their actions as protecting humanity from annihilation by nanotechnology. At the time Operation Fifty was conceived, self-replicating nanobots had become commonplace in medical science, but Erskine, a nanobot engineer, discovered that hostile countries and terrorist groups had released weaponized versions. While these harmful nanobots were imperfect, they had already spread throughout the world and were evolving, so pandemics of increasing lethality were unavoidable. Victor convinced Thurman and Erskine to implement Operation Fifty: destroy human civilization before weaponized nanobots did so, leaving the occupants of the Silos as the only surviving humans while Earth's surface is thoroughly cleansed by benign nanobots. Donald detests his involvement in Operation Fifty, but he continues cooperating since the fate of humanity depends on the Silos' success. He deduces that the linchpin of Silo 18's rebellion is an elderly teacher named Mrs. Crowe, who has an immunity to the amnesia medication, and Silo 18 is reset instead of terminated.
In 2345, Juliette makes her journey from Silo 18 to Silo 17. The Silo 1 staff go to awaken Thurman per protocol, but mistakenly awake Donald instead due to interference by Thurman's daughter Anna. Using Thurman's authority, Donald uncovers that only one Silo out of all 50 is going to be permitted to resettle the world, since Thurman wants to guarantee that no knowledge of nanotechnology or nuclear weapons persists; on E-Day in 2550, the fortunate Silo will be selected by a computer algorithm evaluating numerous variables, and the others will be terminated. Donald decides to avert this so that all Silos live.
Donald's narrative is interspersed with early events in Silos 17 and 18. In Silo 18, the Great Uprising touches off and is quelled with the removal of its ringleader, Mrs. Crowe. A young revolutionary named Mission has his memory wiped, becomes a compliant citizen, and is permitted to start a family. It is implied that Mission is an ancestor of Allison, Holston's wife. In 2312, a rebellion in Silo 17 results in it being terminated by Silo 1, leaving Jimmy Parker, the son of the Silo's IT head, as one of a scant few survivors. Jimmy renames himself Solo.
Dust
Dust is the third and final arc of the series, and is contained in a single book of the same name. It concludes the stories begun in Wool and Shift.
Donald maintains regular contact with Juliette in Silo 17 and Lukas in Silo 18, but his health begins deteriorating rapidly. As the residents of Silo 18 undertake the excavation of a tunnel to Silo 17, Thurman is awakened and reasserts control over Silo 1, resulting in Donald being beaten and imprisoned. The tunnel breaks through to 17 just as Thurman notices that 18 has gone rogue and orders its termination, and only about 200 residents make it to safety before 18 is saturated with poison gas.
Donald's sister Charlotte, who Donald illegally woke up, and a sympathetic security officer named Darcy try to free Donald and escape Silo 1 together. Donald is dying and too weak to leave. He persuades Charlotte and Darcy to go without him, while he plans to set off Silo 1's embedded demolition charges so that the other Silos will be liberated from the tyranny of Thurman and Operation Fifty. Darcy sacrifices himself so Charlotte can make it out safely, and Donald destroys Silo 1.
Meanwhile, Juliette discovers that all Silos possess a tunneling machine that, when activated, will connect them to a place designated "Seed". Silo 17's machine requires more fuel than is available, so Juliette and the other survivors try to walk to Seed over the surface. They emerge from a wall of dust and realize the world has already healed itself. The Silos are enshrouded by an artificial veil of toxic dust, but beyond them, there is breathable air, clean water, and a thriving ecosystem. When Juliette and the survivors arrive at Seed, they find it is a sprawling bunker replete with food, materials, and plant seeds, everything needed to rebuild civilization. Charlotte encounters the group, and Juliette invites her to join them to rebuild the human civilization together.
