The story of Z for Zachariah is all about survival in the face of nuclear annihilation. Young heroine Ann Burden finds herself quite possibly the only human being left on earth after the nuclear holocaust. Left to her own devices for survival in the lonely post-apocalyptic world of Amish country somewhere along the northern Atlantic coast, Ann manages to find not just the means to survive but the will. And then a man in a strange green plastic suit reveals that Ann is not necessarily the only survivor.
This man, who is investigating the contents of the valley, takes his suit off and takes a bath in what is revealed to be radioactive water. He gets extremely sick, and Ann decides to approach him. She takes care of him and nurses him back to health. But the story takes a dark turn when the rejuvenated stranger, Mr. John Loomis (a Cornell-trained scientist that made his way from Ithaca, New York to Ann's valley in search of human life), begins to take charge of Ann, especially because he realizes that he will live. Mr. Loomis' hostile behavior comes to a climax when he attempts to rape Ann. She successfully escapes and runs away to her cave in the woods.
Ann decides that though they cannot live in the same house, she and Mr. Loomis need each other to survive: he has the supplies and she has the knowledge and health to plant the crops, milk the cows, and take care of the house. Mr. Loomis reluctantly agrees to Ann's compromise, in which they split the food on the condition that Ann will take care of the garden, the farm animals, and the general operations of the house and Mr. Loomis is to leave her alone. However, Mr. Loomis soon begins to use Ann's cousin's dog, Faro, to track her and eventually (rather unsuccessfully) shoots her. He also finds her cave and destroys the inventory of food and supplies she has.
At this point, Ann realizes that Mr. Loomis is not going to change, and she does not have the heart to kill him. She decides to steal his safe suit and wagon and leave the valley in search of other human life. She tricks Mr. Loomis, and in their final confrontation she walks away defiantly, expecting Mr. Loomis to shoot her. He does not, and in an act of unusual kindness points Ann to the west, the direction in which he saw birds flying.
