Carolyn, covered in blood from murdering Detective Miner, walks barefoot along Highway 78 toward Garrison Oaks. She encounters an old man in a truck who stops out of concern, mistaking her appearance for an accident involving a horse. She politely declines his offer for a ride, fabricating a story to allay his suspicions, and continues into the woods, reflecting on her home and the librarians' unique reckoning of time under the moon of black lament. She changes into her familiar robe, discarding her ruined dress, and approaches the clearing near the bull statue.
In a flashback, Carolyn recalls her origins as an ordinary American child whose family was destroyed in an attack on Father. Adopted by him along with other orphans, they are trained in ancient catalogs of knowledge. Carolyn, assigned languages, grows bored and rebels, leading Father to let her study grace and movement with a deer named Isha and her fawn Asha in the forest. This period becomes her happiest, forming a deep bond, but ends tragically when David kills Isha and Asha on Father's orders to force Carolyn back to her studies, leaving her isolated and hardened.
Back in the present, Carolyn spies on David, Michael, and Jennifer in the clearing as they dismantle Margaret's grave and resurrect her from a month-long death. The group discusses their month-long search for the missing Father, with no success across realms like the dead, animals, or futures. Other librarians arrive, including Alicia, Rachel, Peter, and Richard, forming a circle to share findings. They ponder Father's possible fate tied to "regression completeness" and note an impending visit from Nobununga, the forest god. David assigns Carolyn to procure an innocent heart as an offering.
The gathering concludes with David gifting Margaret a severed head of a former Japanese Prime Minister, Yamada, whom she animates briefly. Carolyn translates his silent pleas about his family, lying to comfort him while concealing her deep-seated hatred for David and the others, rooted in past traumas, as she maintains a facade of compliance.
Steve Hodgson, a plumber with a history of burglary who's trying to reform his life through Buddhist principles, meets Carolyn at Warwick Hall, a jazz-themed private bar. Carolyn, dressed eccentrically and claiming to be a librarian, propositions him to break into a house to retrieve something precious that was stolen from her, offering him $327,000 in cash. Despite his initial refusal and internal conflict over his past misdeeds and desire for a better life, Steve's financial struggles lead him to agree. They discuss details, with Carolyn assuring him it's a simple residential job involving basic locks and an alarm, recommended by her sister Rachel who knows of his skills.
Steve and Carolyn leave the bar, steal a Toyota Camry from an airport long-term parking lot to avoid using his identifiable work truck, and drive to the target house in a mostly empty subdivision. Steve disables his phone, gathers tools, and breaks into the dark home, which belongs to Detective Marvin Miner, noting the alarm is unset and the owner appears absent. As they search, Carolyn's behavior turns flirtatious, leading to a kiss in the dining room.
Suddenly, Miner emerges from the shadows, appearing disoriented and drugged, and shoots Steve dead with a shotgun while repeating phrases like "You're under arrest." Carolyn, revealing her manipulation, takes the gun, uses Steve's lifeless hand to fire it at Miner, killing him and staging the scene to look like a mutual shootout. She leaves her thumbprint on a light switch plate.
Overwhelmed with remorse, Carolyn cradles Steve's body through the night, apologizing profusely in multiple languages, promising to make things right while rocking back and forth in grief.
Following the murder of Isha and Asha, David returns to the library with their carcasses, which are processed: Carolyn helps skin them without complaint, delivering parts to Lisa for leather and Richard for bowstrings, while Father roasts the meat in a bronze bowl. Despite Carolyn's request for a low-key homecoming, Father hosts a grand feast attended by dignitaries such as the ambassador from the Forgotten Lands and the ancient Strewachin, who rarely manifests in the physical world. Other nobles like the Duke and Liesl join, enjoying the meal under firelight, but Carolyn excuses herself early to study in her cell, avoiding the festivities. Father later tests her progress in languages and expresses satisfaction.
About a year later, around age ten, Carolyn is in her book-lined underground chamber beneath the library, avoiding the outdoors after witnessing the brutal punishment of Rachel, who attempted escape and was torn apart by sentinels for her catalog involving strangling her own children to create ghostly agents for future predictions. Michael, naked and sunburned from studying in the ocean with the sea tortoise Diver Eye, visits Carolyn, clutching a cuneiform manuscript. She hugs him, noting his difficulty with words, and they catch up: she mentions Margaret's deteriorating mental state, David's overly cheerful nature, and her own studies.
Carolyn translates and summarizes the ancient manuscript for Michael, describing a second-century battle marking the dawning of the fourth age. It recounts Father (referred to as Oblaka) initially being defeated by the emperor, but renewed when a former confidant of the emperor, Nobununga, switches allegiance, arriving like thunder from the east to turn the tide, leading to Father's victory.
Michael reveals he will meet Nobununga the next day to begin training with him, saddening Carolyn as he is her closest friend. She confirms Nobununga's name from the text, reflecting on the rarity of good times in the library.
Carolyn awakens in Mrs. McGillicuddy's living room after killing Detective Miner the previous night, carefully masking her true thoughts as the other librarians sleep. She reflects on her age and disconnection from American life, having spent much of her existence in the library under Father's influence. The group has been staying with the elderly widow for six weeks, initially using Lisa's persuasive abilities and Jennifer's drugs to ensure her compliance, but Mrs. McGillicuddy has grown fond of them, enjoying cooking elaborate meals like Eggs Benedict. Carolyn interacts with Jennifer, who diagnoses the widow with a "heart coal"—a metaphorical condition of unresolved grief over her estranged son—while Carolyn acquires hashish for her.
Carolyn signals to Peter about a secret meeting and heads to the Bronze Bull clearing to rendezvous with Michael, Peter, and Alicia ahead of Nobununga's arrival. En route, she encounters a tiger stalking her, leading to a tense chase where she climbs a tree for safety. It turns out to be Nobununga himself, Michael's mentor, who roars and interacts with her before proceeding. Carolyn warns Peter and Alicia about Nobununga's form, and they discuss suspicions that David or others might have harmed Father, given the barrier preventing access to the library.
Nobununga attempts to breach the barrier into Garrison Oaks but succumbs to its effects, collapsing dead after identifying it as a "risak iriel" (the denial that shreds). Michael rushes in grief-stricken to aid him but falls victim to the barrier; Carolyn feigns a rescue, dragging him out while staging her own distress. The group convenes by a stream, where Michael shares Nobununga's insights on the barrier—a mathematical construct anchored by a token and triggered by specific internal experiences, affecting only certain individuals like the librarians but not Americans.
They deduce the barrier's spherical nature and plan to map it using an American to locate and remove the token, acknowledging the need to involve David despite suspicions. Carolyn pretends reluctance but agrees, suppressing her hidden agenda and tremors of deception.
By the third year of her apprenticeship in the library, Carolyn has largely forgotten the outside world, immersing herself solely in studying languages, both real and mythical. She no longer recalls her biological parents' faces and estimates her fluency in tens or hundreds of thousands of languages. While contemplating the Atul concept of "uzan-iya"—the moment an innocent heart first considers murder—she realizes she's hungry and ventures out, discovering the larder empty. Jennifer mentions a marijuana experiment, but Carolyn declines due to an upcoming test and suggests inviting Margaret, noting her deteriorating state.
Carolyn enters a house occupied by "dead ones"—reanimated neighbors who mimic life but lack true consciousness—to get food. She encounters a woman preparing a meal, a girl drawing a disturbing family scene, and a boy watching television, which evokes memories of her pre-library life. The dead ones' disjointed interactions unsettle her, reminding her of Father's resurrections, possibly incomplete like Margaret's frequent deaths. She eats quickly and leaves, only to face a sudden storm signaling Father's return.
The children gather as Father confronts them about Margaret learning "gon iriel," a pain-denial technique from David's catalog, violating rules against sharing knowledge. Father punishes David by locking him in a bronze bull grill and burning him alive over two days, forcing the others to tend the fire. David's screams echo through the night, but he endures due to his training in survival. Jennifer resurrects him over seven days, healing his charred remains while the group assists.
Post-resurrection, David becomes quieter and more cruel, breaking Michael's arm over a trivial dispute. During a feast with courtier Mont Strouachen, Carolyn observes David's hatred toward Father, recognizing it as his own "uzan-iya." She realizes David will eventually attempt to kill Father and begins pondering how to use this to her advantage.
Erwin Charles Levington, a former Army sergeant major turned middle school art teacher and now Homeland Security agent, reflects on his unconventional life—from enduring childhood bullying over his name to heroic acts in Afghanistan that inspired a book and movie. Disillusioned after years of combat, he finds solace teaching kids, particularly helping a bullied student named Deshawn, whose Christmas card profoundly impacts him. Seeking purpose beyond teaching, Erwin joins Homeland Security to investigate anomalies, leading him to a Virginia county jail to interview Steve Hodgson, accused of murdering Detective Miner.
At the jail, Erwin encounters recognition from staff familiar with his military fame, including a deputy's brother he saved in combat. He meets Steve's public defender, Larry Dorn, who shares crime scene details and dismisses Steve's story of a mysterious woman named Carolyn. Erwin reveals connections: Carolyn's fingerprints link her to a bizarre $327,000 bank robbery in Chicago, where tellers voluntarily assisted her and an accomplice (possibly Lisa) without coercion, captured on video. He shows photos tying Carolyn and Lisa back to childhood, suggesting a deeper mystery with sparse records post-age eight.
During the interview, Steve recounts his encounter with Carolyn, confirming details but denying the murder, expressing remorse over a past incident involving a friend. Suddenly, chaos erupts: screams and gunshots signal an attack. A blood-soaked man in a tutu and flak jacket—David—bursts in, kills Dorn brutally with a chained spear, and abducts Steve after a cryptic exchange recognizing Erwin's fame. Erwin arms himself but arrives too late, finding carnage. He smokes a cigarette in the chapel, pondering a childhood photo of Carolyn that includes a young Steve, as thunder approaches.
Elianne, a Brazilian model, attends a party at the lavish Connecticut estate of rapper Marcus (Little Z), hoping to secure a spot in his music video. Marcus, eager to impress, leads her to his private zoo featuring two lions: the massive male Dresden and his half-grown daughter Nagasaki (Naga). He boasts about capturing them in Africa, where he killed their mother and darted the father. As they prepare to "fish" with live chickens as bait, Elianne grows uneasy in the dark, landscaped forest, sensing something amiss.
The lions' pits are empty, and panic sets in as branches crack nearby. Dresden emerges and attacks Elianne, killing her swiftly and painlessly in a hunter's merciful way. Marcus, terrified, flees to the underground husbandry room for safety but finds Carolyn, the naked Michael, and the bloodied David (in a tutu) waiting inside. They've orchestrated the lions' escape as part of a deal with Dresden.
Carolyn explains their arrangement: in exchange for freeing Naga and allowing Dresden time to exact revenge on Marcus for invading his home, murdering his mate, and imprisoning them, the lion will protect their "agent" as his own cub. Dresden desires a hateful kill, binding Marcus to immense suffering without release to the afterlife. Marcus pleads futilely as Carolyn and Michael retreat, leaving David to oversee his fate while Dresden and Naga approach.
Steve awakens disoriented in a 1980s-style teenage bedroom in Mrs. McGillicuddy's house, piecing together his abduction from jail by the bloodied man in the tutu (David). He changes into outdated clothes and enters the living room, encountering eccentric librarians: the sleeping David, the trance-like Margaret flicking a lighter, and the couple Peter and Alicia. Carolyn arrives, introducing everyone, while Mrs. McGillicuddy offers fresh cinnamon rolls. Steve confronts Carolyn about framing him for Detective Miner's murder, expressing fury over his ruined life and potential death penalty.
Carolyn apologizes, claiming unavoidable circumstances, and outlines her plan: Steve must jog to her family's house at 222 Garrison Drive to retrieve an unknown object—a token anchoring a "risak iriel" barrier that repels her family with escalating pain or death but spares outsiders. She demonstrates her power by calling the White House, using secret codes and blackmail to secure a presidential pardon for Steve, verified by a code phrase ("old lang syne") in a live press conference, with Rachel's future visions aiding authenticity.
Steve remains skeptical, accusing Carolyn of lies about the object's nature (a mathematical construct in the "plane of regret") and her motives, suspecting her father's enemies or even her father set the barrier to block access to a library of sensitive books. Carolyn equips him with a gun against potential sentinels (bodyguards) and assures protection from David's skilled allies. Trapped with no resources and facing recapture, Steve reluctantly agrees, noting the need for cellphones to stay in touch—something Carolyn pretends to know about.
Steve Hodgson begins his jog along Highway 78 toward Garrison Oaks, aware of his fugitive status from news reports. Equipped with a duct-taped holstered pistol, spare magazines, and a Bluetooth headset connected to Carolyn via cellphone, he cautiously approaches the subdivision sign, testing for any adverse effects from the "risak iriel" barrier. Feeling nothing unusual, he proceeds deeper, noting the unremarkable neighborhood with modest houses and old cars. He spots dogs, including a Bernese Mountain Dog named Thane with mismatched eyes, and reports to Carolyn, who warns him to ignore them.
As Steve reaches the first intersection, the dogs—now including a Beagle, Labs, and a German Shepherd—attack ferociously upon his advance. Thane bites his arm, and others latch onto his limbs, inflicting severe wounds. Steve fights back, using his pistol but missing initially. Two lions, Dresden (male) and Nagasaki (female), arrive as backup, roaring and engaging the dogs to protect him. Steve retreats, dropping a magazine in panic, and shoots several dogs amid the chaos.
Limping to a nearby white brick house, Steve enters for safety, finding it empty except for medical supplies, food, and water as promised by Carolyn. The lions follow him inside after fending off the horde. Outside, hundreds more dogs gather, but the lions stand guard. Steve tends his wounds with bandages and antibiotics, while an elderly woman inside repeats nonsensical greetings, oblivious to the situation.
Steve communicates with Carolyn, who confirms the lions are allies and urges him to stay indoors for a day or two. Amused by the absurdity, Steve laughs hysterically as the lions settle in, ignoring him while the woman offers to take his coat repeatedly.
Erwin Levington arrives at the White House, encountering a stern secretary and meeting General Dan Thorpe, who recognizes his military fame. Ushered into the Oval Office, Erwin briefs the President, Secretary of State, Chief of Staff Brian Hammond, and others on his jail encounter with the bloodied man in a tutu (David) who abducted Steve Hodgson. He connects this to Carolyn Sapasky, linking her fingerprints from Miner's murder scene to a bizarre Chicago bank robbery involving cooperative tellers and an accomplice possibly named Lisa. Erwin describes David's speed, weaponry, and recognition of him from Natanz, speculating on motives and mentioning the name "Nobunaga."
The group discusses Carolyn's direct call to the President demanding Hodgson's pardon, using classified codes and blackmail. Erwin suggests the events are orchestrated for leverage, advising caution rather than immediate retaliation, as Carolyn anticipates tracing and reaction. He notes Hodgson's apparent innocence and normalcy, contrasting with the operatives' eccentricity. The meeting reveals high-level concern over "Cold Home" files and potential terrorist ties.
Post-meeting, Erwin annoys the secretary while waiting. Thorpe requests a debrief, but the President recalls Erwin for thanks and a personal chat, bonding over shared personas of feigned simplicity. Erwin questions the President's public "dumbass" image, leading to mutual laughter and an invitation to a bi-weekly card game.
Steve Hodgson, at around age twelve, loses his parents in a fatal car accident that leaves him in a coma for six weeks. He awakens with no memory of the crash, suffering only minor burns and a concussion. His Aunt Mary takes him in, providing a trailer home life marked by neglect, alcoholism, and poverty. Steve, grieving and angry, adapts poorly—facing bullying at his new school, shoplifting, and eventually committing burglaries to cope with his circumstances.
Steve's criminal activities escalate, focusing on jewelry and valuables pawned through a fence named Quiet Lou. He befriends Jack, a wealthier classmate with a rebellious streak, and they become burglary partners. Steve integrates into Jack's stable Mormon family, finding temporary solace, but their crimes lead to Jack's arrest for drug dealing. Jack serves time without implicating Steve but endures prison hardships, ultimately committing suicide after three months.
Devastated, Steve attends Jack's graveside service from afar, where Jack's mother, Celia, confronts and slaps him, calling him an "asshole." This event solidifies Steve's self-loathing and guilt, haunting him as a profound "nothing" that defines his existence, echoing in his thoughts and actions long after.
Steve converses with Carolyn via phone while tending to the wounded lioness Naga, expressing frustration over her delayed rescue and his injuries. He administers a suppository to himself for blood loss, feeling immediate improvement, and then applies one to Naga despite the awkwardness. Dresden, the male lion, watches protectively but allows it. Steve hangs up angrily on Carolyn after she dismisses Naga's importance, turning off the phone to ignore her calls.
As Naga shows signs of recovery but continues bleeding, Steve decides to save her, vowing to escape despite the risks. He explores the house for options, finding an unused Ford in the garage on flat tires. Hearing a mail truck, he briefly hopes for aid, but it leaves upon seeing the dogs. More dogs gather, prompting Steve to call a taxi service, negotiating a ride for $500 he doesn't have, planning to commandeer it with his gun.
The Yucatan Taxi arrives, and Steve shoots a dog on the porch, pulling the driver inside for safety. He loads the unconscious Naga into the minivan, urging Dresden to follow, but the lion stays to delay the horde of dogs, sacrificing himself. Steve drives away heartbroken, leaving Dresden buried under attacking canines.
Harshen Patel, the cab driver trapped in the bathroom after bites from the house's undead residents, is rescued by Carolyn. She repays his inadvertent aid to Steve with a duffel bag of cash, warning him of an impending plague involving Barry O'Shea and tentacled beings, advising him to flee to a well-lit urban high-rise with supplies.
Steve flees Garrison Oaks in the stolen Yucatan Taxi minivan, with the injured lioness Naga in the back, realizing the vehicle's bloodied state and his excessive speed. Spotting a veterinary clinic in a strip mall, he pulls in to seek urgent help for Naga's severe wounds from the dog attack. Inside Black Path Animal Hospital, Steve, desperate and armed, coerces vet techs Jerry and Allie, along with Dr. Alsace, to treat Naga, assuring them no harm if they comply. Despite skepticism and fear, they anesthetize and suture the lioness, while Steve tends his own injuries.
Erwin arrives at the clinic, recognizing Steve as the fugitive, and arrests him after negotiating Naga's safety, promising to arrange care at a zoo or shelter. En route to DC, Erwin detours to a vantage point overlooking a military raid on Mrs. McGillicuddy's house, where Carolyn's group hides. The assault, involving Delta Force, SEAL snipers, Bradleys, and helicopters, turns catastrophic: David slaughters the intruders with inhuman speed, downing helicopters and massacring soldiers in a bloodbath visible from afar.
Carolyn ambushes Erwin and Steve, revealing she anticipated the raid and orchestrated events, including extinguishing the sun to unleash chaos from the Third Age—plagues, reality viruses causing tentacle mutations, and indestructible entities called silent ones. She explains Father's ancient conquests, his library's infinite power over reality, and the ongoing struggle for control in this Fourth Age. Carolyn recruits Steve to confront David, who is en route to assassinate the President, amid the darkening world.
As the sun fades completely, plunging the afternoon into starlit night, Carolyn warns of adapting to the apocalypse while prioritizing seizure of the library. Steve, coerced but intrigued, agrees to accompany her back to Garrison Oaks, grappling with the cosmic stakes and Carolyn's manipulations.
Carolyn awakens in her room after being resurrected by Jennifer following a brutal assault and murder by David. Disoriented and in pain, she initially reacts aggressively but calms down, realizing Jennifer is helping her recover. Jennifer examines her wounds, including a shattered jaw and stabbed forearms, confirming Carolyn's first death and explaining memory gaps. Carolyn feigns distress while concealing her true composure and a hidden book from David's catalog, ensuring Jennifer doesn't suspect her secret studies.
As Jennifer probes Carolyn's emotional state, suggesting she exhibits signs of a madness common among librarians—seeking to maximize suffering as an avoidance mechanism—Carolyn deflects by appearing vulnerable and tearful. She recounts the assault, portraying it as David's twisted attempt at seduction, but internally focuses on protecting her illicit knowledge. Jennifer shares her own experiences with David and Father, revealing a lenient punishment for neglecting her duties, hinting at her value as the primary resurrector.
Carolyn, alone after Jennifer leaves, bathes rigorously to cleanse herself of the trauma, rejecting further social invitations. Using the Al-Shaq Irkun technique to become invisible (though blinded), she navigates the library to return a borrowed book from David's war catalog and acquire another on vengeful murder strategies by Adam Black.
She reads late into the night, finding solace in plotting revenge against a superior foe, her actions marking a calculated step toward subverting Father's rule.
Steve stops the car near Garrison Oaks, where Carolyn identifies David, Erwin, and Margaret under a streetlight. Carolyn reveals her plan to confront David alone, insisting Steve proceed to the library for safety, as the risak iriel barrier will protect him. Despite Steve's protests and offers to help, Carolyn emphasizes his inability to face David, who is martially superior. She kisses Steve goodbye and walks toward the confrontation, leaving him and Naga to sneak into the subdivision.
Under the streetlight, Carolyn admits to killing Father and orchestrating the risak to David, who reacts with surprise and amusement. As David attacks, Carolyn lures him deeper into the risak's perimeter, enduring spear wounds and torture to exploit its escalating pain. Erwin, recovering nearby, loads a found magazine into his pistol and shoots David in the face at Carolyn's calculated moment, inflicting a fatal wound. Carolyn then shocks David's brain to induce eternal agony before freezing him outside time using altered physical constants.
Margaret, holding the President's head, accepts Carolyn as her new "mistress" and requests death in the bull for a chance at redemption. Despite Steve and Erwin's objections, Carolyn fulfills this, sending them away. Erwin stays behind, while Steve and Naga head to the library. Carolyn joins them, explaining her manipulations ensured David's defeat, and they enter the library's threshold amid gathering dead ones and animals.
As they cross, the door opens into darkness, with Carolyn receding rapidly. Steve, hesitant but compelled, follows with Naga, stepping into the unknown passage.
Steve enters the library through the doorway at 222 Garrison Drive, experiencing no disorientation beyond stepping into a vast, pyramid-shaped structure filled with endless bookshelves. Carolyn greets him, explaining the library as a separate superset universe overlapping with normal space, created by Father for protection. The jade floor alters distance, aiding navigation, while the structure spans miles with catalogs on various subjects like mathematics and alternate geometries. Steve, overwhelmed, questions the physics-defying scale, and Carolyn clarifies it's not magic but advanced knowledge.
They ascend a massive spiral staircase toward a glowing cloud of lights representing the normal universe. Steve examines ancient books, including one on alternate geometries depicting battles against otherworldly creatures. Carolyn reveals Father's catalogs cover immortality, war, and more, written over millennia. Steve grapples with the implications, while Naga accompanies them cautiously.
At the summit, a jade platform offers a view of the universe. Carolyn hangs David's frozen, black-enshrouded body in space, explaining it will become a heat-emitting but lightless sun due to eternal anguish energy. Steve, horrified, demands explanations for his involvement. Carolyn admits manipulating events, including his clumsiness to drop a magazine for Erwin, as part of her long-term plan against Father and David.
Carolyn offers Steve any gift from the library's power—immortality, invincibility, intelligence—revealing her debt to him. They share a picnic with extinct scorpion-like meat, discussing the library's origins and Father's conquests. Carolyn recounts her traumatic childhood, adoption after parents' deaths, and Father's brutal training, including blinding Michael repeatedly. Steve, compassionate, recognizes her suffering shaped her ruthless actions.
Carolyn descends to the dormitories carrying a box of popcorn, Everclear, and Marlboros, hoping to improve her strained relationship with Steve. Over a month has passed since the events at Garrison Oaks, and Steve has grown increasingly dissatisfied with the library's peculiarities, including its floating furniture, glowing jade floors, and bizarre catalogs. He spends his time playing video games, exploring with Naga, or traveling to places like the Serengeti, often avoiding Carolyn. She reflects on her initial fantasies of their life together, now replaced by Steve's resentment and her own demanding responsibilities consolidating Father's catalogs.
Steve opens the door warily, still fearful of Carolyn's power. They share popcorn, but tension arises as Steve questions her hairstyle and studies. Carolyn offers more materials on lion dialects, but Steve shifts to the dire state of the outside world under the black sun—famines, riots, earthquakes, and societal collapse—blaming her indifference. He reveals contacting Erwin and the President, urging her to watch news reports of global chaos, including food riots and gravitational disruptions from the library's projection.
Carolyn admits overlooking the crises amid threats from Father's enemies like Q33 North and Barry O'Shea. Steve, drawing from Irwin's advice, confronts her emotional detachment as a survival mechanism from her traumatic past, likening it to lacking a common vocabulary for normal human experiences. He pours Everclear over himself and ignites it with Margaret's lighter, committing suicide in a final act to pierce her "heart coal" and awaken her compassion, leaving Carolyn horrified and alone as Naga prevents intervention.
Carolyn repeatedly resurrects Steve after his suicides—first from burns, then a slit wrist, heart failure due to a mismatched blood type, and finally liquid plumber ingestion—but ultimately leaves him dead after the last attempt, overwhelmed by grief. Immersed in her studies on reality viruses, she discovers a mis-shelved brown folder containing the ancient craft of Al-Shaq Shabaleth, a technique to make slow things swift, invoked quickly with a word. An illustration warns of its dangers, and a note in Father's handwriting directs her to a specific book in Jennifer's catalog on elixirs, specifically the Font of Perfect Memory. Suspicious of coincidence but intrigued, Carolyn prepares the elixir over days of trial and error, consumes it, and begins contemplating Adoption Day.
The elixir grants Carolyn vivid recall of Labor Day 1977, when she was eight, waking in her parents' home, eating breakfast, making potato salad, and heading to a neighborhood picnic. They chat with Adam Black (Father) on his deck, where he's grilling on the bronze bull, discussing his retirement from a "book business" and training a successor named Carolyn, unknowingly referring to her. The picnic unfolds with children playing, including Steve, David, Michael, and Margaret, evoking Carolyn's innocent crush on Steve and their shared bookish interests.
As a Pershing missile approaches, Father invokes Al-Shaq Shabaleth, accelerating the children while time slows for adults. The missile detonates into a fireball, vaporizing parents and homes; Carolyn and Steve struggle uphill to safety behind Father, burning from air friction. Steve heroically pulls Carolyn to safety despite severe burns, which Father heals with ointment. Other children reach Father, who absorbs the blast.
Father declares the children orphans and adopts them as Pelapi apprentices, assigning catalogs: languages to Carolyn, war to David (his biological son, destined for cruelty), exploration of the dead to Margaret, and others accordingly. He sends Steve away to live with his aunt, planting him as a "coal" in Carolyn's heart for future strength, then leads the children into the library, promising to make Carolyn a god as she reluctantly takes his hand.
Carolyn ventures into Jennifer's dusty apothecary to gather rare supplies for resurrecting Father's mummified body, reflecting on nostalgic memories and her grief over lost siblings. After weeks of arduous work, she succeeds, and Father awakens, praising her for outmaneuvering him and expressing pride in her as his heir. They discuss her elimination of the other librarians, including the difficult choice with Michael, and Father explains his orchestration of events to ensure her rise. He offers insights on Steve's suicidal tendencies, suggesting options like altering the past to unite them or abdicating her power for a normal life, while revealing his retirement plan to create a new universe with resurrected allies Nobununga and Mithragani.
Father recounts altering history multiple times, roasting innocents in the bull to forge a successor, ultimately choosing Carolyn over David because she never begged during trials, proving her unbreakable strength. He hands her the black folio, a powerful artifact for changing the past, and formally ends the Fourth Age, bequeathing the library to her before ascending the Jade Staircase. Carolyn then resurrects Steve in the penthouse, where they reconnect over shared childhood memories unlocked by her actions. Inspired by Steve's compassion, she reveals plans to restore the world—calming volcanoes, providing cloud-derived bread to end famine, and normalizing orbits—declaring him the savior of billions.
Using an ancient word, Carolyn transforms Steve into a new, brighter sun, encasing his head in energy to dawn over Earth. She relocates to an Oregon farmhouse facade of the library, finding warmth in a pink robe and cartoon cat slippers left by Father. There, she discovers Michael alive, accompanied by wolves and a cougar, who initially submits in fear but warms to her invitation inside. As they eat and rest, the new sun rises, melting winter's ice and heralding spring—the librarians' second moon of kindled hope—while Carolyn watches over them, smiling with renewed peace.
Erwin serves a ten-year sentence at USP Big Sandy for assaulting and holding the President hostage to force a nuclear strike on the library pyramid, amid global food shortages following the sun's blackout. Surprisingly content in prison, he enjoys a clean cell, books funded by admirers like Deshawn, and respect from inmates and guards due to his military fame. Minor altercations are swiftly handled, and letters from old comrades provide comfort, making his regimented life reminiscent of basic training. As rations improve with sky-falling bread, Erwin settles into reading, including a Janet Evanovich novel, until lights out interrupts him.
One night, Carolyn emerges from the floor, grabbing his wrist and materializing fully in his cell. She expresses surprise at his imprisonment, and Erwin explains his actions stemmed from Steve's failed persuasion and the need to end the apocalypse. Carolyn, unfazed by the nukes she missed due to her busyness, offers him freedom and a job involving errands like locating Steve's deceased cocker spaniel, Petey, promising to teach him library secrets such as her bank manipulation technique.
Michael's voice warns from the toilet of approaching enemies, speaking in an unfamiliar language before Carolyn translates. As rumbling destruction and screams echo in the hall, signaling Father's old foes mobilizing against her, Carolyn urges a quick decision. Erwin eagerly accepts, grabbing only his book, and takes her hand to escape, with Carolyn assuring him she has a plan against the dangerous threats.