Plot
Ann Burden, the seemingly sole survivor of a recent nuclear apocalypse, lives an agrarian life on her family's valley farmstead with her dog. She is sheltered from the radioactive contaminants outside the valley by rocky hillsides, favorable weather patterns, and an abundant supply of ground-fed water.
One day, Ann encounters another survivor, a man named John Loomis. He claims to be an engineer, who, aided by medicines and a radiation suit, walked from a distant government bunker to Ann's valley. John unknowingly bathes in a radioactive spring, and immediately becomes sick with radiation poisoning, but is nursed back to health by Ann, who welcomes him into her home.
John regains his strength, and gradually, becomes part of Ann's humble rustic life. He helps Ann pump diesel from local petroleum pumps and gets the farm's long-disused tractor running to expand her gardens for the winter. Ann tells John about her parents and younger brother who left the valley to find other survivors, but never returned.
John speculates that he could generate hydro-electricity to power the farmhouse’s dead generator from the nearby waterfall, by using a water-wheel fashioned from the Burden chapel’s planks and beams. Ann is uncomfortable with this proposal, citing her father's involvement as preacher and her own deeply-held Christian beliefs. John chooses to not pursue the project further.
Ann and John grow closer, cultivating crops and preparing for long-term winter habitation. Their domestic accord is marred by occasional tensions, notably involving matters of religion and John’s drinking. The two come to the verge of initiating a sexual relationship, but John declines, claiming a sexual relationship will change them, and he needs more time.
Mysterious phenomena, including missing eggs and glimpses of a shadowy figure at the chapel, culminate in the arrival of a third survivor, a man named Caleb. Although Ann welcomes Caleb into the house, John resents Caleb, stating "whites belong with whites". John questions Caleb's backstory and motives, while Caleb repeatedly emphasizes the religious connection he shares with Ann, in stark contrast to John.
The three survivors slowly settle into a marginally-stable partnership. Both men share post-apocalyptic horrors they witnessed before reaching the valley. John describes a radiation-poisoned child begging him for death and that he couldn't bring himself to oblige. Caleb describes watching the other underground miners kill each other in a fit of claustrophobic paranoia.
Later, John privately confides to Ann his belief the dying boy was her long-absent brother and confesses to having killed him out of mercy. Caleb pressures Ann to go forward with the water-wheel project, and work commences on tearing down her father's chapel for materials.
Perceiving their mutual attraction, John awkwardly gives Ann consent to pursue a romantic relationship with Caleb, but belies his grief and anger in losing Ann through his remarks. Shortly thereafter, following a celebratory dinner, a heavily intoxicated John tells Ann he loves her before passing out in a bedroom in Ann's home. After failing to wake John, seeming to want his affection, Ann joins Caleb in the adjoining bathroom, where the two engage in sexual activity. The two men finish the water-wheel, moving it and its wooden flume into place atop the waterfall. Encumbered by the bulky radiation suit, Caleb slips twice during his rope-assisted climb up the mossy cliffside. During the second slip, the two men silently lock eyes, both holding the rope, while Caleb teeters on the cliff's edge.
John returns to the farmhouse alone. Ann apologizes for her earlier indiscretion and John claims Caleb left in search of other settlements. Ann takes this news badly, chasing after Caleb but not finding him, and lapses into a sullen silence. The farmhouse's electric lights and refrigeration are restored. Ann realizes John has moved her beloved church organ and three pews into the barn. Ann, playing a hymn on the organ, exchanges a glance with John and he prays behind her.
