''Z For Zachariah'' is a 1975 novel by Robert C. O'Brien (the same author who wrote ''Mrs. Frisby and the Rats of Nimh'', later made into ''WesternAnimation/TheSecretOfNIMH'' by Creator/DonBluth). It's a [[AfterTheEnd post-apocalyptic]] novel for young adults, following sixteen-year-old Ann Burden, who believes she's the only survivor of a nuclear war that seems to have wiped out the rest of the world. For a largely [[HandWave unexplained reason]], the valley in which she lives seems to have escaped the nuclear fallout, meaning she's able to make it on her own.

A year after the war, another person, a man named John Loomis, finds her valley. He's survived thanks to [[{{Technobabble}} a suit]] he designed before the war, a prototype of a radiation suit that had been planned to be mass-produced before the war interrupted it. He gives himself radiation sickness by bathing in a contaminated stream, leaving Ann to take care of him. At first he seems okay, but as he gets better he becomes more and more controlling and downright creepy, culminating in an attempt to rape Ann.

She runs away to the other side of the valley, where she tells him she will stay once she's finished taking care of the agricultural work and tending to the animals. What follows becomes a cat-and-mouse game with Loomis trying to force her to return, locking the small store where their seeds and fertilizer must come from, taking away the key to the tractor, and eventually trying to shoot her so she can't run away. Eventually she manages to steal the suit while he's out, and confronts him just before she leaves the valley, telling him that if he shoots her he really will be alone. Realizing he'll never get her to stay, he tells her he saw birds circling to the west, and the book ends with her writing in her journal, "I am hopeful."

There was a BBC made-for-tv movie in 1984, and a big-screen adaptation was released in 2015, starring Creator/MargotRobbie, Creator/ChiwetelEjiofor and Creator/ChrisPine. The first trailer can be viewed [[https://youtu.be/5k5tlNHUCj0 here]].
!!This novel provides examples of:

* ActualPacifist: Ann has a gun of her own, and has several opportunities to shoot Loomis, but ultimately decides to leave instead.
* AdamAndEvePlot: Ann considers this, but discovers Loomis was there ahead of her when he tries out the attempted rape listed below.
* AdaptationalAlternateEnding: [[spoiler:The film ends with Ann and Loomis deciding to carry on living together without yet looking for other survivors.]]
* AdaptationDecay: The film removes the cat-and-mouse nature of Ann and Loomis's relationship (as well as the latter's increasingly villainy) in favor of more of a LoveTriangle with a post-apocalyptic backdrop.
* AdaptationExpansion: The 2015 film introduces a third survivor, a man named Caleb.
* AdaptationalHeroism: Loomis is portrayed much more sympathetically in the 2015 film.
* ApocalypseHow: Class 2, bordering on Class 3.
* AfterTheEnd: Nuclear and biochemical warfare appear to have wiped out most of the human race.
* AgeLift: Ann is a teenager in the novel, but a grown woman in the film.
* AloneWithThePsycho: Unfortunately for Ann.
* AttemptedRape: Fortunately for Ann, Loomis is still so radiation-sick she fights him off without much difficulty.
* BadDreams: Both Loomis and Ann have them, though Loomis's tend to be much worse because of the reason that caused his SanitySlippage, as listed below. Ann's are simply the result of having lost her family and everyone she knew thanks to the war.
* BolivianArmyEnding: [[spoiler:The novel ends with Ann venturing out of the valley and into the radiated zone, looking for other survivors. She's hopeful about her fate and has a dream of her teaching that ''may'' be DreamingOfThingsToCome, but it's equally likely that she'll become sick and die, just as the rest of the population, as well as her own family, did.]]
* BreakTheCutie: Loomis tries to do this, but ultimately fails, largely because Ann is a lot saner and more practical than he is.
* TheCaretaker: Ann, while Loomis is dealing with the radiation sickness.
* ConvenientlyAnOrphan: In the books, Ann is orphaned after her family likely dies while investigating further out; her being AloneWithThePsycho wouldn't be nearly as effective with a family around.
* [[UsefulNotes/NuclearWeapons The Deadliest Mushroom]]: Takes care of most of the world.
* DeadlyGas: It's stated that nerve gas was used in addition to nuclear weapons.
* DepopulationBomb: Created the deadly mushrooms.
* TheDitz: Loomis regards Ann as this, and indeed initially shows himself to be much smarter, working out such things as how to use the fuel pumps without power (i.e. ReadTheFreakingManual). Unfortunately he fails to show similar cleverness in interpersonal relations, trying to force the issue when Ann shyly asks if he used to be married.
* DownerEnding: [[spoiler:The film. Loomis [[KarmaHoudini gets away with likely]] [[MurderTheHypotenuse killing Caleb]], with Ann apparently none the wiser. Having no other alternatives, and despite having stronger feelings for Caleb, she stays with Loomis and the two apparently start a new life together.]]
* DreamingOfThingsToCome: Possibly. At one point Ann dreams of a classroom of children she's teaching, and it's implied that it might be a dream of what she'll find once she's left the valley.
* DrivenToVillainy: It's implied that Loomis didn't become a monster until the war hit.
* TheEndOfTheWorldAsWeKnowIt: Big time.
* EpistolaryNovel: The entire narrative is written in the form of Ann's journal.
* EverybodysDeadDave: Ann initially thinks this; later, once she's discovered she's not the only one left, she has great cause to ''wish'' it was true.
* {{Foreshadowing}}: While he's still sick and hasn't yet showed any real signs of creepy, Loomis says, "Ann Burden, you'll wish I'd never come here." Boy, does he turn out to be right.
* GrowingUpSucks: It definitely does when you're one of the two survivors of nuclear holocaust, and the other is arguably half-crazy.
* HammerAndSickleRemovedForYourProtection: The enemy in the war is never named. Given the time the book was written, it was probably intended to be the Soviet Union, but a modern reader might be equally tempted to assume [[MakeTheBearAngryAgain modern Russia]], [[UsefulNotes/RedChina China]], or even UsefulNotes/NorthKorea.
* HandWave: Why the valley has survived the fallout is never really explained.
* HiddenSupplies: Ann stocks a cave with supplies when Loomis first arrives, just in case she needs to hide for an extended period of time. This comes in handy later.
* IdiotBall: Loomis survives in a nuclear wasteland for a year, yet doesn't think to check the radiation level of the water before he takes a bath in it.
** Arguably justified. There were two streams in the valley; one uncontaminated (it rose from a spring in the valley) and one contaminated (it flowed in from the outside). When Loomis arrives in the valley, he discovers the first stream and tests it, finding it to be uncontaminated. Being unfamiliar with the valley, he is unaware that there are two streams and when he returns to take his bath, he does not realize that he actually come to the second (contaminated) stream.
** You Fail Health Physics Forever- there's no way a stream could be that contaminated a year after the war so as to be able to give a person radiation sickness by bathing in it.
* KarmaHoudini: [[spoiler:If Loomis did kill Caleb, he's this by the end, living with Ann with no more competition, and with her apparently none the wiser of his deeds.]]
* LaserGuidedKarma: Loomis greatly fears being alone, but it's his actions that drive Ann to leave. In the book he begs her not to go, in the film he begs her to come back someday. She quite reasonably points out that her leaving is entirely his fault.
* LoveTriangle: Between Ann, Caleb, and Loomis in the film.
* TheMovie: A made-for-TV movie was produced in Britain in 1984. The setting was changed to Wales, but much of the rest of the story was left unaltered. A big-screen movie starring Creator/MargotRobbie, Creator/ChiwetelEjiofor and Creator/ChrisPine was released in 2015.
* MurderTheHypotenuse: [[spoiler:Implied with Caleb.]]
* PartingWordsRegret: Sort of. Ann's last words to Loomis before she leaves for good are that he never even thanked her for taking care of him, something she thinks back on later as being "childish" of her.
* RaceLift: Loomis in the film.
* SanityBall: Ann is definitely the only one holding this.
* SanitySlippage: This happened to Loomis long before he found the valley, thanks in part to the fact that he [[spoiler:shot his friend and fellow survivor for wanting to take the suit and check on his almost certainly dead family]].
* ShootTheDog: Literally; after realizing Loomis is using her dog to track down her scent, Ann has no other choice.
* StalkerWithACrush: Stalker with ''something'', anyway; Loomis is awfully intent on catching Ann again, but it's implied that it's largely because he's such a control freak.
* TitleDrop: Played with. When she was a little girl, Ann had a Bible ABC book in which A was for Adam, the first man, so she assumed Zachariah was the last man.
* WorldWarIII: It lasted approximately [[TheShortWar two weeks]] before everything died.