Nightfall

Theremon goes to the Apostles of Flame headquarters, a golden tower in the city’s affluent quarter, to meet with Mondior 71. Theremon is led by a black-robed monk into a secret chamber, where he meets the group’s public relations officer, Folimun 66. Theremon insists on meeting Mondior in person, but Folimun assures him that Mondior is busy preparing for the imminent apocalypse.

Theremon decides to ask Folimun some questions about the nature of the apocalypse. Referring to the Apostles’ scripture, The Book of Revelations, Folimun shares the group’s beliefs about the Darkness that will obscure Kalgash’s six suns and the Stars that will burn the planet. Theremon asks for proof, but Folimun simply provides the age of their organization, dating back several millennia, which gives them firsthand experience of the previous obliterations. Theremon asks Folimun what can be done if it is too late for mankind to repent and seek the mercy of their gods. Folimun answers that their objective is twofold: they want people to convert to their teachings and to protect themselves from the Stars, so that they can be part of the next cycle of civilization.

Folimun excuses himself, expecting that he and Theremon will meet again. Before leaving, he asserts that while he is a self-avowed fanatic and cultist, he is not a “madman.” Charmed by Folimun’s self-deprecation, Theremon takes home a copy of the Apostles’ scripture.

Sheerin returns to Saro by plane, continuing to experience the claustrophobia that struck him in the Tunnel. He starts to feel better as he leaves the terminal, where he is picked up by a colleague, Liliath 221. Liliath notices that Sheerin has lost weight since he left for his trip. She asks him how his trip went, so Sheerin reports his experiences, downplaying the horrors of the Tunnel. He asks in turn how things have been at the university, which prompts Liliath to tell him that Beenay 25 has been looking for him. Sheerin is familiar with Beenay because his partner, Raissta 717, is Sheerin’s niece. During the drive back to the university, Sheerin once again experiences claustrophobia and a loss of appetite.

Siferra returns to Saro University to analyze a series of tablets recovered from the Hill of Thombo. She shows Balik tablet markings that she believes to be part of an intelligible script. Balik tells her that word has gotten around about their discovery of the layered cities, which has led to some skepticism from their department colleagues. This upsets Siferra, but Balik reassures her that the controversy around her findings speaks to their potential impact. Balik suggests going on vacation together before they resume their work. Siferra declines, however, preferring to keep their relationship professional.

Mudrin 505, a paleographer at the university, comes by to examine the Thombo tablets. Siferra shows him the photos of the site and shares her theory that the underground cities are much older than Beklimot. She presents the tablets to Mudrin, who recognizes some of their markings. He asks to take them to his lab for further study. After Mudrin leaves with the tablets, Balik tries to apologize for his vacation idea. Siferra disregards him.

Beenay tells Theremon about the outcome of his meeting with Athor. He shares how he and Athor have gone deeper into theorizing what the unknown factor might be. Sheerin joins the pair for drinks, and he and Theremon are introduced to one another. Sheerin tells them about his experience at the Exposition. Beenay then tells Sheerin about their current work on Universal Gravitation. Sheerin laughs at the possibility they may be trying to revise the theory to fit their data, comparing them to the Apostles of Flame. At this point, Theremon shares details about his visit to the Apostles’ headquarters, including Folimun’s predictions about the Stars and the apocalypse. Sheerin invites the possibility that their prediction could have merit.

Athor’s wife, Nyilda, tries to convince him to come home to take a break, but Athor is too compelled by his work to leave the observatory. Yimot comes to hand Athor some calculations and notices the director’s hand trembling from exhaustion. He offers to bring him a snack, but Athor declines.

Athor reviews the postulates he has developed to explain Beenay’s findings. None of them make sense, however. He enters Yimot’s calculations into his computer, which returns compelling evidence that the unknown factor hypothesis is correct. He calls the other astronomers and shares his theory: A previously unknown planetary body orbits Kalgash, influencing its orbit around Onos. This satellite is invisible to the naked eye, and so the astronomers decide to use astrophotography to determine the exact position and orbital trajectory of the satellite, which Beenay calls Kalgash Two. Beenay muses over the possibility of Kalgash Two coming close enough to block out any of the planet’s suns, resulting in Kalgash’s first-ever eclipse. Having reached a clear course of action, Athor decides to go home.

Beenay visits Siferra at her office, where she tells him about her discovery at Thombo. Siferra shares her theory that each layer of settlement seemed to have existed for roughly 2,000 years before its respective destruction. Siferra also presents Mudrin’s findings on the Thombo tablets, explaining that each one contains an account of a city’s divine obliteration.

Beenay realizes that Siferra is trying to get him to recognize the prophecies of the Apostles of Flame from these accounts. Siferra explains that she needs Beenay’s advice, considering that the tablets seem to validate The Book of Revelations. Remembering what Theremon had told him about Mondior’s predictions, Beenay confirms her suspicions. Siferra allows some room for doubt, stressing that the past doesn’t always guarantee the future. However, Beenay tells her the exact date of the apocalypse, as communicated to him by Theremon.

Siferra implores Beenay not to tell Theremon anything about her findings, afraid that validating the Apostles will become her new legacy. Beenay continues to recall the Apostles’ prophecy, then remembers how it includes a passage on the world being cast into total darkness. This sparks a realization in him, and he leaves immediately after promising to keep Siferra’s discovery a secret.

Beenay approaches Faro and another astronomer, Thilanda, to calculate the historical trajectories of Kalgash’s six suns over the last two millennia and their projected trajectories for the two millennia to come.

As he studies the suns on Athor’s computer, Beenay begins to imagine a scenario where only one of Kalgash’s suns illuminates their side of the planet. Beenay supposes that even if the sun in question were Dovim, the weakest one, the scenario would not produce conditions of total darkness.

Thilanda transmits the projections to Athor’s computer, at which point Beenay tries to calculate how often Kalgash Two might eclipse Dovim if it were the only sun in Kalgash’s sky. Although it is extremely rare, Beenay concludes that this scenario is possible, resulting in total darkness on Kalgash once every 2,049 years. This calculation precisely matches the date of the Apostles’ prophesized doomsday.

Athor gathers Beenay, Sheerin, and Siferra in his office to discuss their respective findings.

Sheerin begins by discussing the way an extended period of darkness caused by the total eclipse of a lone sun will result in “universal madness,” whose symptoms include disorientation, depression, and the loss of reason. To elaborate on this effect, Sheerin imagines the possibility of a world with only one sun, causing it to cycle between light and dark on a more regular basis. The people on this planet would be accustomed to periods of total darkness, unlike the people of Kalgash, who have only ever experienced perpetual sunlight. He demonstrates the effect by having Beenay obscure all light from the room and instructing him to find the psychologist’s chair. Beenay struggles to do so and eventually begins to succumb to claustrophobia after a few moments. Sheerin notes that the effect was much worse for the Tunnel of Mystery survivors, who had stayed in total darkness for 15 minutes. Beenay suggests that people can resist the effects of total darkness, but Sheerin chastises him for his hubris, stressing he is not yet capable even of imagining total darkness.

Siferra goes next, explaining that her reluctance to share her conclusions was allayed by Beenay’s findings on the eclipse of Dovim. She shares photographs and charts of the Thombo excavation and describes the destruction of each city layer by fire. Having radiocarbon-dated charcoal from each layer of the excavation site, Siferra confirms that each fire occurred at precise intervals of 2,049 years, the same amount of time between each eclipse of Dovim and between each doomsday predicted by the Apostles of Flame. Sheerin points out that with the loss of reason, people will resort to fire for light, suggesting that this is what destroyed each civilization.

Athor indicates that the evidence presented offers a scientific basis for the Apostles of Flame’s Book of Revelations. The next step, he tells them, is to see how they can use the Apostles’ predictions to ensure humanity’s survival. Beenay protests that some parts of their prediction are incomprehensible, such as the existence of the Stars. Athor clarifies that he does not mean to validate the Apostles, but to see how their data can help them ensure survival through science. Siferra suggests turning their findings over to the government, but Sheerin replies that administrative bureaucracy will be too slow to prepare for doomsday.

Beenay argues that working with the Apostles will damage their professional reputations as scientists. Though this causes Athor to withdraw his initial suggestion, Beenay realizes that he can use Theremon’s connection to bring Athor and one of the High Apostles together. Athor is hesitant to trust a journalist with such sensitive information, but he agrees. He instructs Sheerin and Siferra to bring him relevant literature on the psychological effects of Darkness and the Thombo excavation. Siferra asks for more time so that Mudrin can finish deciphering the tablets.

Athor stresses once more that he does not mean to validate the Apostles, but to use what knowledge the group has to their advantage. He advises the other three to distance themselves from mysticism in the same way.