The movie opens with a Montage establishing the white, red, and yellow stars around a brown desert planet. Narration (by James Barry Blakely) and a Montage of characters establishes Sor (Alexis Kanner), the Blind Seer, and Aton (David Birney), the city leader and scientist, as well as their conflict, which smoothly segues into Sor's archeological discovery; a sealed metal casket he claims dates from a mythical "eighth nightfall". Zol (Russell Wiggins), Sor's assistant, shouts at Bet (Starr Andreeff), Aton's daughter, who has been eavesdropping during their discovery, that this is proof of what the Book of Illumination claims.
Ana (Andra Millian), known as "that woman" for most of the film, has walked into the city from apparently nowhere and Aton has been mesmerized by her. Aton's supporters kidnap her and exile her to the desert to get Aton to focus on his duties as city leader. Roa (Sarah Douglas), Aton's ex-wife, has joined Sor's religion. He elevates her to his level by having hawks peck out her eyes and teaching her to read the Book of Illumination. Boffin (Susie Linderman) has been working on a new type of telescope, one that makes sounds based on how far away objects are. With this "telescope for the blind", she discovered the "dark sun", a new celestial body alongside the known white, red, and yellow suns.
Tensions rise, crowds of people grow frightened of the growing cold, and the two city leaders fight frequently. The only thing that everyone agrees on? Nightfall is coming, and it will be The End of the World as We Know It.
Nightfall provides examples of:
- Arcology: The Trope Namer no less — Aton's city was filmed in Arcosanti in the Arizona desert.
- Adaptation Deviation: The film changes the cast of characters dramatically (two characters use names from the original, but really aren't the same at all), and the New Age technology really helps sell the "alien world" concept. Turning the planet into a desert, adding in Psychic Powers, and lots of sex divorces it heavily from the original story.
- Adaptation Name Change:
- There is still an Aton and Sor from the original story, but they are wildly different from their original characterization and no longer have last names.
- The Book of Revelations has also been changed to the Book of Illumination, to match with the temple being the Temple of Illumination.
- The city's original name is Saro, and the planet was named Lagash, but in this film, everyone calls it the city or our planet.
- Because this film only has half as many stars, they are named based on their colour (white, red, and yellow) instead of Greek letters.
- Adaptation Personality Change:
- Aton, astronomer and scientist, is now the local city leader. He spends the first part of the movie obsessed with a mysterious woman, and stubbornly insisting that they live in a city of light.
- Sor, religious leader and off-screen antagonist, is now given screentime equal to Aton. He seems to encourage archeology and preparations for the coming Darkness, but he is still obsessed with his cult, and ritualistically blinds his followers by having hawks eat their eyes.
- Affectionate Nickname: Bet's mother calls her Betta as a sign of affection.
- Alien Sky: The planet orbits three suns; yellow, red, and bluish-white stars. People of the city have seen clouds, but had never lived without sunlight. When Boffin invents a "telescope for the blind", it works by making sounds, and she discovers a "dark sun", what we would call a moon.
- Apocalypse Cult: Sor teaches his followers that it is only through prayer and faith that they will survive the ninth nightfall despite the planet being swallowed by Darkness.
- Blind Seer: Sor, the leader of the religious cult, is a blind man (who even dons the occasional blindfold). His prophecy of Darkness is believed by many, making him the second most important person in the city. One of the characters points out that the power of prophecy isn't in how accurate they are, but in how much they are believed. In this case his blindness is plot-relevant, as thanks to Endless Daytime only the blind have learnt to navigate a world where they can't see. He even blinds his followers to prepare them for the coming Darkness.
- Everybody Has Lots of Sex: Multiple sexual encounters are shown on-screen, with several more implied. An impressive feat, given the lack of romance and female characters in the original story.
- Eye Scream: One of the rituals practiced by Sor's religion is tying down a member and letting hawks peck out their eyes. Roa's screaming indicates that they're not likely to have any sort of anesthetic.
- Femme Fatale: "That woman" genuinely isn't trying to harm anyone, but her attractiveness and sensuality drives first Aton, then Kin, into becoming madly in love with her. She's exiled from the city by Atom's supporters during the first act because he's no longer providing the leadership they want from him. Kim is sent out into the finally manages to learn her name is Ana.
- Foil: Sor and Aton have a number of similarities. Sor is a blind man leading a religion, while Aton is a visionary scientist who leads the city. Aton privately admits to "that woman" that when he was younger, he used to have poor vision and blackouts. He noticed that his eyesight improved as he studied astronomy by watching the stars. This is the inverse to Sor, who deliberately blinds the people who follow him so they won't see the Darkness during the upcoming nightfall. The two leaders give charismatic speeches to their followers and engage in debates multiple times throughout the film. Roa used to be married to Aton, but Sor has seduced her away and makes her his equal in their religion.
- Montage: During the opening credits, a variety of three star arrangements are shown against a dark background. There's a white, red, and yellow star around a brown planet. The montage continues by showing short pans across the desert landscape of "our planet", then switching between characters until the end of the Opening Monologue.
- A Mythology Is True: The Book of Illumination predicts that the three suns will set and the planet will enter a cave of Darkness. Sor, the blind prophet, is leading archeological excavations to prove accuracy of the prophecies.
- New Age: This production dressed the characters in robes, created machines from crystals, shells, and strings, and built up the idea that strong emotional ties were opposed to scientific pursuit. Dr Asimov's reaction to this style was to distance himself from this movie as much as possible.
- One-Word Title
- Only One Name: Despite Aton having a daughter and an ex-wife, all of those relationships are revealed through dialogue, rather than family names. Even Sor, the opposite of Aton in most ways, who essentially marries Aton's ex-wife, doesn't have any name other than Sor.
- Opening Monologue: After the opening credits, narration over Montage establishes Aton and Sor as the people in control of the city, and their conflicts.
- Psychic Glimpse of Death: Because Kin suspects a Psychic Link connects Ana and the snake, he takes her and snaps her spine, killing the snake and throwing it away. Ana is twisted and cries out in pain. It looks like her back is broken, too, but it's only the pain because her will is broken and when she goes back to the city with Kin, she's perfectly healthy again.
- Public Bathhouse Scene: Aton and the mysterious woman (Ana) have sex in a large outdoor bath. It might even be Aton's private bathhouse, to show rich he is.
- Romanticism Versus Enlightenment: Aton represents Enlightenment through his optimism and scientific devotion, while Sor represents Romanticism through his doomsaying and religious devotion. The film itself pulls firmly towards Romanticism by having Sor be unquestioned in his authority while Aton's supporters undermine him by insisting science is fiction and betraying him to Sor. It also shows Aton's over-indulging in lust/love through his obsession over "that woman".
- Science Hero: Aton is definitely charismatic, but his charisma is geared towards inspiring people towards building and preserving, rather than to persuasion or violence. Sor is able to convert Aton's followers to the Temple of Illumination, but Aton builds machines out of kites.
- Suck Out the Poison: After sex, Kin and Ana have fallen asleep in a cave, when a snake comes around and bites Kin on the leg. Immediately Ana sucks and spits the venom out to save him.
- Title Drop: Sor, the religious leader, has come to argue with Aton, the scientific leader. Aton insists that he be told what Sor has planned, and Sor talks about the stories in the Book of Illumination, identifying the upcoming eclipse as nightfall. The secret holy book tells him that this event has occurred several times before."This... night... fall... will be the ninth nightfall and the darkness one of all."—Sor
- Title Sequence: The opening starts with a Montage of three star arrangements shown against a dark background. There's a white, red, and yellow star around a brown planet. The montage continues by showing short pans across the desert landscape of "our planet" while the last of the credits are shown before the Opening Monologue begins.
- Tomes of Prophecy and Fate: Sor's Book of Illumination is written in a sort of Braille that holds the record to previous nightfalls, and Sor is able to convince people that the future is recorded as well. Halfway through the film, he blinds Roa and begins teaching her the writings of the book so that she can be a Blind Seer like him.
- Two Scenes, One Dialogue: While Sor and Aton are rallying their respective followers about the upcoming nightfall, the movie switches between the two monologues, creating plenty of Dramatic Irony as Aton encourages his followers to prepare by creating an underground sanctuary and Sor encourages his followers to prepare by praying to prove their faith.