The Obelisk Gate

Essun spends the book sheltering in Castrima, the underground geode comm led by the orogene Ykka, where she is reunited with Alabaster, her former mentor and lover, who is dying: his body is slowly petrifying as a consequence of the magic he used to fracture the continent at the end of The Fifth Season. Before he fully turns to stone, Alabaster teaches Essun about the obelisks and about magic, the silver, life-generated force that actually underlies orogeny. He explains that his goal in breaking the world was to generate enough power for a sufficiently strong orogene to use the network of obelisks — the Obelisk Gate — to pull the lost Moon back into orbit, which would end the recurring Fifth Seasons for good. As his body fails, he and Essun also reconcile over the long-ago death of their child. In his final act, Alabaster expends the last of his strength to stop Essun from accidentally killing everyone in Castrima while she is overwhelmed by obelisk power, and then dies, turning completely to stone.

Castrima is soon besieged by a raiding army from the rival comm Rennanis, which locates and threatens the geode's hidden ventilation shafts to force the population into the open. With no other option, and aided by a faction of hostile stone eaters working against Rennanis, Essun uses the training Alabaster gave her to open the Obelisk Gate herself, drawing on the power of obelisks across the world. She uses this power to turn every person in the attacking Rennanis force to stone in an instant, saving Castrima. The victory comes at a cost: the battle has irreparably damaged the geode's magical life-support systems, so despite having survived, Castrima's people know they cannot stay and begin preparing to leave and search for a new home as the Season worsens.

In parallel, Nassun's father Jija discovers her older brother Uche is an orogene and beats him to death in a rage; realizing Nassun is likely orogenic too, he abducts her and flees their hometown, intending to take her south to a group of Guardians rumored to be able to "cure" orogenes. After a hard journey through a landscape devastated by Alabaster's continent-splitting, they reach Found Moon, a settlement of Guardians led by Schaffa — Essun's former Guardian, who survived her attack at the end of the first book with severe amnesia but has regained enough memory to resume protecting young orogenes. Nassun bonds intensely with Schaffa, who becomes a father figure to her, and rapidly develops both her orogeny and her perception of magic, eventually learning to draw power from a nearby obelisk. During this training she accidentally kills a fellow student, turning him to stone in a nightmare-induced surge of power. When Jija realizes Nassun has not been "cured" and is in fact growing more powerful, he confronts Schaffa and then tries to kill Nassun himself; she turns her own father to stone to survive. The book closes with Essun's group in Castrima abandoning their ruined home to search for safety, and Nassun, having lost both her brother and father, remaining at Found Moon under Schaffa's protection, her formidable powers still growing — with mother and daughter's separate paths left unresolved and unconverged.

Essun — the powerful orogene protagonist, formerly known as Damaya and Syenite — spent this book in Castrima, an underground comm run by the orogene leader Ykka, who allows orogenes to live openly. There she reunited with Alabaster, her former Fulcrum mentor and lover, whose body was slowly turning to stone from the magical toll of having fractured the continent at the climax of the first book, triggering the current Fifth Season. Alabaster taught Essun about obelisks and about magic — the silver, life-derived energy underlying orogeny — and revealed that his ultimate goal is to use the Obelisk Gate to pull the long-lost Moon back into orbit, which he believes would end Fifth Seasons permanently. He died by the book's end, turned fully to stone, after using his last strength to stop Essun from losing control of obelisk power and killing everyone in Castrima. Traveling with Essun is Hoa, who appeared as a mysterious "child" since the first book and is now confirmed to be a stone eater; another stone eater, Antimony, was loyal to Alabaster and seemed at odds with Hoa and with a rival faction of stone eaters allied with the enemy comm Rennanis. Castrima was attacked by a Rennanis raiding army late in the book; Essun, using Alabaster's teaching, opened the full Obelisk Gate and turned the entire attacking force to stone, saving the comm — but the fight destroyed the geode's magical life-support systems, so as the book ends Castrima's people are preparing to abandon their home and search for a new settlement amid the worsening Season.

Meanwhile Essun's ten-year-old daughter Nassun has been on a separate, unconnected journey. Her father Jija discovered her older brother Uche was an orogene and beat him to death, then, suspecting Nassun was orogenic too, abducted her and fled their hometown of Tirimo, seeking a rumored group of Guardians who could "cure" orogeny. They ended up at Found Moon, a Guardian-run settlement led by Schaffa — Essun's own former Guardian, who survived her attack in book one but suffered severe memory loss and has only partially regained his sense of purpose. Nassun grew close to Schaffa, who became a protective father figure to her, and she rapidly developed her orogenic and magical abilities, learning to draw on obelisk power, though she accidentally killed a fellow student with it during a nightmare. When Jija realized she had not been "cured" and was growing more powerful, he confronted Schaffa and then attacked Nassun directly; she turned him to stone to defend herself. As the book ends, Nassun is left at Found Moon under Schaffa's care, her power and understanding of magic still rapidly growing, having lost her brother and now her father.

Going into the next book: Essun and Nassun remain unaware of each other's exact circumstances and have not reunited; Essun's group is setting out from a ruined Castrima to find a new home; Nassun's abilities are advancing dangerously fast under Schaffa's guidance at Found Moon; Alabaster is dead but his knowledge and goal — using the Obelisk Gate to capture the Moon and end Seasons for good — has passed to Essun; and the true nature and loyalties of stone eaters like Hoa and Antimony, as well as the rival stone-eater faction, remain open and unresolved.