12 Miles Below recap

Keith Winterscar's attempt to recover old technology awakens a buried facility and drops him and his father, Tenisent, into a vast machine realm. Their escape forces Keith to rely on the technical instincts Tenisent once dismissed, while Tenisent confronts his failures as a father. A mysterious guide leads them to Journey, an Imperial relic armor that accepts Keith and grants him unusual access. Tenisent dies after Keith defeats an adaptive machine hunter, but Tenisent's own armor later moves and fights in a way its stored model cannot explain. A rescue party reaches Keith, recovers a hidden yellow sphere, and battles toward the surface while Relinquished directs machines against them. Atius appears to die holding To’Aacar behind sealed doors, then revives outside. Kidra inherits Winterscar, Keith survives with Journey, and evidence that Tenisent may persist through the armor's soul fractal gives Keith a new purpose.

Keith Winterscar survives a torn environmental suit underground, then the account returns to the expedition that brought him there. He and his older sister Kidra neglect their assigned harvest to explore a buried control room. Keith accidentally reactivates a defensive turret, and Tenisent, their father, destroys it in Winterscar relic armor. Kidra shields Keith from blame, but Tenisent responds harshly and threatens to remove Keith from future expeditions unless he produces an exceptional harvest. A rival, Anka Shadowsong, offers Keith a rare antenna handbook as the prize in a power-cell contest against Kidra's occult knife. The convoy then changes course at the command of Atius, its Deathless clan lord, who senses an unexplained call from the west. The destination is an ancient complex. Anka's drone gives her an early advantage, while Keith enters through a damaged roof with Tenisent as his assigned escort. Keith identifies the central structure as a data center, but blocked lower routes leave Anka closer to the expected transformer rooms and put Keith behind in the wager.

Keith finds twelve spent power cells in the data center and secretly restores backup power. The system detects Relinquished attempting to breach it, starts erasing protected information, and ignites buried rockets. Their failure collapses the complex into a vast sinkhole, stranding Keith and Tenisent in a shifting underground city maintained by Mites. Winterscar is badly damaged, Tenisent's left arm is unusable, and their surface search window is short. Keith studies the Mites and traces power to a terminal that may provide a route out. Screamers interrupt the attempt. Tenisent destroys most of them despite his injury, but the last machine incapacitates him and nearly kills Keith. Tenisent recovers in time to finish it, then uses a dangerous stimulant to keep moving. Keith powers the terminal and operates it through old command syntax. It gives them a map and a route from a location roughly twelve miles below the surface. Tenisent carries Keith toward the outskirts, increasingly trusting the technical judgment he once dismissed.

The journey reopens the family's past. During an earlier slaver raid, Tenisent saved Keith and Kidra but left much of Winterscar to be destroyed or captured. He then spent years training his children with punishing severity. In the present, he kills a speaking drake and explains that a vast, unstable generation of Deathless now threatens civilians and underground settlements. Keith and Tenisent enter the Underpassage, following its upward routes until an awakened machine nest blocks them. Both are injured during their escape, and Tenisent loses his rifle. Gold-flashing doors then guide them into a crypt containing an intact masterless relic armor, an occult sword, and the remains of an Imperial crusader. Keith takes the armor because his ruined environmental suit cannot support a surface return. The armor identifies itself as Journey, accepts him as its wearer, and begins monitoring and assisting him. Its medical link also reveals the full extent of Tenisent's condition: the arm concealed within Winterscar is missing, not merely disabled.

Journey predicts that Tenisent's internal injuries will become fatal without treatment. While training Keith in armor movement and occult weapons, Tenisent admits that he treated Keith's analytical learning style as weakness and made instruction punitive. An unknown Root Administrator grants Keith elevated access to Journey. Keith uses similar controls in Winterscar to create a functioning simulated arm from Tenisent's recorded movements. The pair recover a black device marked as the former crusader's highest priority. Her locked message asks that her evidence reach the Solaris Imperium, but its password and the device's purpose remain unknown. They contact Atius's rescue party, which now includes Kidra and Anka after both defied orders to join the search. Before reunion, an adaptive spider automaton ambushes Keith and Tenisent and collapses a bridge beneath them. Their sealed armor carries them through an underground river into a welded city farther from help. They find an elevator upward while Tenisent's stimulant approaches the point where it may impair his mind. During the ascent, he accepts Keith as a relic knight and takes responsibility for abandoning his children after their mother's death.

The adaptive spider reaches Keith and Tenisent with a force of Screamers before the rescue party can arrive. Journey's targeting and movement assistance let Keith fight effectively, but the spider impales Tenisent through the abdomen. Keith refuses his order to flee. He gives Journey full control of his body, kills the machine, and uses every available medical supply, but Tenisent dies after their reconciliation. Keith repairs Winterscar enough to carry Tenisent's body and reports the death to Atius. More Screamers trap him in a building. As his barricade fails, he asks Winterscar to run Tenisent's stored combat model. The armor unexpectedly rises, releases an occult pulse, fights with Tenisent's technique, and produces a voice it lacks the recorded data to imitate. Journey detects an unexplained power surge and a surplus associated with the armor's soul. Atius, Kidra, Anka, and the rest of the rescue party finally reach Keith. Atius compares the pulse to a Deathless soul strike but cannot explain it. The group performs Tenisent's burial rite, and Keith publicly honors his father as true of heart. The armor's apparent agency remains unresolved.

Tenisent's body disappears from Winterscar before Kidra inherits the armor. Its refusal to reshape blood-stained areas deepens Keith's suspicion that it retains more than a predictive model. The party collects enough machine power cells to refuel its airspeeder, then follows Atius to a flooded Imperial bunker. Inside, Keith, Kidra, and Atius recover a yellow sphere tied to an elite Solaris Imperium order. The yellow guide contacts Journey through it and reveals itself as a researcher who digitized both mind and soul. It claims responsibility for guiding Keith to Journey, causing the original collapse, and granting his administrator access. It also identifies Relinquished as the ancient intelligence commanding all machines except Mites. Before Relinquished interrupts the contact, the guide unlocks Journey's former crusader logs and gives Keith a mission recording plus coordinates for a hidden book about soul fractals. That work may explain whether Tenisent's soul remains within Winterscar. Atius takes custody of the sphere and orders its existence concealed.

Atius deceives Relinquished long enough to learn that the new Deathless are imperfect copies and that chosen agents have been prepared against them. As a machine army converges, Atius secretly gives the yellow sphere to Keith while maintaining a false hard-drive story. The party retreats through the bunker. Keith restores its defenses, and Winterscar independently activates the full turret bank, again suggesting an unexplained connection to Tenisent. At the closing blast doors, the machine champion To’Aacar blocks the escape. Kidra recovers the sphere from Keith's damaged pack and carries it through after it confronts her with memories of her choices. Atius stays behind, cuts off To’Aacar's hand with an occult blade, throws the weapon to Keith, and appears to die while the doors seal the champion below. The survivors reach the surface and are extracted with their power cells and concealed cargo. At the original site they find Atius alive, restored by his Deathless revival but missing his armor. He privately summons Kidra about the sphere. Keith enters weeks of medical treatment with Journey, Atius's blade, the unlocked crusader evidence, and the guide's unopened mission. Tenisent is physically dead, but Keith commits to finding the soul-fractal book and investigating whether his father persists within Winterscar.

Keith, Kidra, Anka, and the remaining rescue party reach the surface with the recovered power cells and the concealed yellow sphere. Tenisent is dead, but Kidra has inherited Winterscar, whose independent actions and response to its former wearer remain unexplained. Atius, believed killed while delaying To’Aacar, revives and returns without his relic armor. He privately calls Kidra to discuss the sphere. Keith keeps Journey, Atius's occult blade, the former crusader's newly unlocked evidence, and the yellow guide's unopened mission recording. His injuries require weeks of treatment. His next objective is the hidden work on soul fractals, which may explain whether some part of Tenisent remains within Winterscar. Relinquished still commands the hostile machines, To’Aacar remains alive below, the new Deathless crisis is unresolved, and the sphere's reaction to Kidra remains secret.