In Wool, mechanic Juliette Nichols became sheriff of Silo Eighteen after Holston followed his wife Allison to death outside. Her investigation exposed the false green landscape shown inside cleaning helmets and the defective suits that killed their wearers. Better materials enabled her to reach abandoned Silo Seventeen, where Jimmy Parker, known as Solo, had survived with a handful of children; while she restored its pumps and contacted Lukas Kyle, rebellion against IT chief Bernard Holland killed Mechanical chief Knox and her friend Marck. Juliette returned, survived the airlock fire that killed Bernard, and became mayor and Lukas's lover. Shift revealed that Donald Keene had designed the silos for Senator Paul Thurman before the nuclear catastrophe of 2052, while Anna Thurman and Mick Webb separated him from his wife Helen. Frozen sleep and memory-suppressing drugs sustained Silo One's operators through centuries of controlling the other silos, whose populations were being assessed for a future only one would inherit; even One's people were expendable. Awakened under Thurman's identity, Donald protected Eighteen, killed Anna without understanding her attempt to enlist him, secretly woke his pilot sister Charlotte, and shot Thurman. Donald's worsening illness, Charlotte's drone reconnaissance, and a destination called Seed left a possible escape to pursue, but Juliette distrusted the people controlling her world.
Dust opened with Eighteen rebuilding after rebellion, a large birth lottery promising new families, and Juliette determined to rescue Jimmy and the children. Lukas searched the servers and the Legacy's histories while she uncovered a huge digging machine behind Mechanical. Courtnee's crew used the backup generator to drive a tunnel toward Seventeen, leaving their own silo dependent on its main generator. Walker developed a portable radio; Shirly and Kali struggled with exhausted workers, and Marck's death burdened Shirly's friendship with Juliette. Father Wendel condemned the existence of other silos as blasphemy, while Lukas and Sheriff Peter Billings urged caution. Juliette wanted space, freedom from reproductive restrictions, and a registered relationship with Lukas. The tunnel reached Seventeen, and her separate surface expedition produced samples and another narrow escape from an airlock fire. Tests showed that outside air damaged inferior suit materials especially badly near the silos. Hidden supply pipes and supposed argon pointed to outside control; Donald recognized destructive nanos behind cleanings and exterminations, while Juliette noticed her scars disappearing. Courtnee brought Jimmy and the children to Eighteen, where Dr. Nichols examined them and Elise acquired Puppy. Their refuge proved cruel: Marcus fell twenty levels to his death, Rickson was injured, a vendor seized Elise's Memory Book, and looting in Seventeen alienated Jimmy. In One, Captain Brevard discovered Thurman alive and exposed Donald's unauthorized actions. Imprisoned and beaten, Donald learned how computers controlled births and ranked populations, and suspected Anna had helped Forty resist the extermination he had ordered. When One demanded Bernard, Lukas sent Security chief Sims to impersonate him. The deception failed, Sims died, and Eighteen's outer doors opened to poison. Juliette directed refugees into the tunnel; Courtnee and Dr. Nichols evacuated the children, and Shirly forced Juliette to safety before sacrificing herself to collapse the passage. Lukas left shelter to tell Juliette he loved her over the radio one last time. Charlotte meanwhile discovered a map converging beyond the silo complex, stole radio parts, and killed Eren when he attacked her, suffering a wounded shoulder. Her transmission reached Juliette in Seventeen: Donald was a prisoner, Thurman was their enemy, and Seed might lie beyond a limited poisoned region. Juliette stopped Courtnee reopening the contaminated tunnel, but took explosives toward One with Raph, seeking revenge. Scarcity and coercion threatened the refugees from within. Father Remmy frightened Elise into revealing the library; her signature was used to declare her Mr. Rash's wife, and Jimmy and Shaw rescued her from a congregation performing invasive procedures on women. A priest burned Jimmy's books and attacked Juliette; Raph freed her, but their escape destroyed the radio connection. Officer Darcy captured Charlotte, then helped Donald after drone footage showed real grass outside the wasteland. Anna's records exposed deliberately collapsible silo floors and her concealment of Forty's resistance; Donald suspected repairing nanos had saved Seventeen. Dying, he took a bomb toward One's reactor while reserving the escape suits for Charlotte and Darcy. Darcy was shot freeing the obstructed drone lift and sent Charlotte upward alone. Thurman intercepted and shot Donald at the reactor, but Donald fired into the bomb; aboveground, Charlotte escaped as One collapsed. In Seventeen, Juliette chose survival over vengeance. The diggers' original bearings and available plans suggested a common destination, but food would last days and tunneling would take weeks. She proposed walking outside, openly admitting the uncertainty. Some survivors stayed to claim farmland; volunteers assembled nearly 150 suits and shared air supplies, with no more than ten people to a bottle. As they cleared the exit, Dr. Nichols and Juliette puzzled over preserved bodies, the children's health, her healing scars, and injuries she should not have survived. With no complete explanation and no time to wait, the party set out through the poisoned dust.
Juliette's group emerged from the haze into blue sky and living grass. Raph, Dr. Nichols, Bobby, Fitz, Rickson, Hannah and her baby, Elise, and Shaw reached the open countryside together, still tethered to their shared oxygen bottle. Other groups followed, including one carrying a limp body. Juliette stopped anyone removing a helmet and urged them farther from the boundary, where plants withered against the dust. From a separate ring of hills she could see that the darkness formed a vast dome over the fifty silos, with green land and a forest beyond it. Dr. Nichols insisted on testing the air first. He removed his helmet, breathed safely, and smiled; everyone began freeing one another from their suits. The children played in the grass, Elise released Puppy, and Shaw produced her book. Juliette was already thinking of saving the seeds from their food when her father pointed out a vine-covered concrete tower in the basin. She used her dynamite to open its door, which had been designed to open from inside. The bunker held clothing, tools, canned food, and labeled packets of seeds, many unfamiliar even to Elise's book. Its twenty closely spaced levels ended at a bare cavern apparently intended to receive a digger. Courtnee traced the electrical feed to silvery sheets on the roof and restored power; a moving platform in the stairwell then made hauling supplies easier. Juliette insisted they take only what they needed and leave provisions for possible later arrivals. Jimmy and Walker struggled to assemble a tent; Walker, who had initially stayed inside his suit until its oxygen ran out, was adjusting to being outside. The little more than one hundred survivors debated settling beside the warehouse or moving farther away. Elise used her book and the sun to identify north and urged them toward the sea, where she believed they could catch fish. Juliette wanted a home beyond the shadow of the poisoned dome. Before they left, a lone suited woman stumbled down the hill and collapsed. Juliette released her helmet and discovered Charlotte, the voice that had told her the truth. Instead of anger, she felt kinship, welcomed her, and invited her to join their journey toward the water. By the epilogue, the travelers have spent days discovering the open world and are camping among trees. Raph hesitates to burn precious wood until the others point to the forest around them. Jimmy has shot a deer, and his reading and practical knowledge have made him a capable leader; Juliette thinks he would make an excellent mayor and intends another vote. The campers consult Elise's book about unfamiliar animal cries. Under the stars, Juliette grieves Lukas, and Elise invents a constellation for Puppy before inviting her to name a human-shaped one. Juliette says that figure already has a name. Later Courtnee brings a remarkable hot drink from their supplies and sits with her. Juliette credits Lukas with supporting the ambitions the silo's rulers suppressed, and finds hope in the immense space available to them. Asked whether they will survive, she answers with confidence that they can build a life of their own choosing.
Juliette and the survivors are camped in the forest on their way toward the water on Elise's map, with Charlotte among them, Jimmy supplying food and guidance, and Courtnee sharing Juliette's hopes and grief. Their supplies and seeds offer a beginning, but they have yet to reach the coast, plant crops, or establish a permanent home. Juliette still mourns Lukas and is considering passing leadership to Jimmy. Others remain in Seventeen, and the surviving silos' circumstances are unknown. Around the camp, unfamiliar creatures call beyond the firelight. The world has room for them; making a lasting home in it is now their own responsibility.