The Character Focus for section one is David, a scientist, who returns to the Shenandoah Valley, and his family, in the wake of a global crisis. Crops are failing, mysterious diseases are showing up everywhere, and animals and people are becoming infertile. Working together with his old teacher, Walt, and other scientifically-trained members of his large extended family, David works to develop blight-resistant crops and plays a critical role in formulating cloning technologies first for animals, then for people. Testing later generations of clones, David and Walt discover that, while clones past the fifth generation are nonviable, the fourth and fifth generations produce greater numbers of fertile members, who can sexually reproduce.
They and the other "elders" (non-clones) assume that the clones share their feeling that sexual reproduction, and the resulting genetic diversity, is a desirable goal. When the first clones (fourth- and fifth-generation girls) become pregnant, David learns this assumption is mistaken. The clones instead intend to form a clone-based society, with the fertile members as mere fallbacks. David attempts to prevent this by destroying the cloning technology, but he is prevented, and subsequently exiled.
Section Two's Character Focus is Molly, implied to be the clone-descendant of David's cousin Celia. Like everyone else in the Valley, she is a member of a clone-family, and has five clone-"sisters," all identical to her, all of whose names all begin with "M." Like them, she is an artist, and her ability to accurately reproduce what she sees is the reason she is named to an expedition to the "outside world," specifically Washington, DC. She will produce maps and sketches that will help future expeditions to forage for the technological supplies the Valley urgently needs. Following the expedition, Molly finds that she has become an individual, unable to subordinate herself to the needs of her clone-family. She bonds with Ben, another member of the expedition who develops a similar problem. Their son, Mark, becomes the Character Focus of the third section and the epilogue.
As the only individual in the Valley, teenage Mark is a loner, but his ability to tolerate, and even thrive during, separation from others — along with the survival skills he learned from his mother and from books — makes him essential to the community, which is planning more foraging expeditions to meet their desperate need for supplies. Though he is incapable of fitting in with, or even of fully understanding, clone society, Mark does what he can to help. But eventually he realizes that his destiny, and any future humankind may have, lies elsewhere.
Winner of the 1977 Hugo Award for Best Novel.
This novel contains examples of:
- Apocalypse How: Class 3B. Most of the Earth suffers Natural Human Extinction, along with some Species Extinction. Narrowly averted in the Valley through use of cloning technology.
- Character Focus: Primarily David, Molly, and Mark, but also Ben, Ben's brother Barry, and Molly's sister Miriam.
- Clone Degeneration: A significant problem for the clone culture. Eventually clone degeneration causes the newest members of their society to lose valuable skills, and finally the abilities of abstract conceptualization and creative problem-solving.
- Clones Are People, Too: The generation which creates the clones never considers that the clones might develop goals which are different from those of their creators.
- Cloning Blues: Averted. The clones are valued by their human creators, and even develop a view of themselves as the next step in evolution.
- Crazy Jealous Guy: Mark, especially by the standards of the clone community. What makes it worse is that they (even Susan, his girlfriend) really have no concept of an exclusive relationship.
- The Dividual: Clone families are extreme versions of the Twindividual variant. Not only are they physically identical, they have the same skills, the same tastes, and the same functions in the community. With the exception of the eldest of each family (who is head of the family) and, briefly, the expedition members, people are almost never seen separately from their family units. It's implied that they can't even achieve sexual satisfaction if the entire family is not participating in the act.
- Driven to Suicide: Molly. She considers the alternative to be a Fate Worse than Death.
- Individuality Is Illegal: One of the truisms of the clone community is "What is right for the community is right even unto death for the individual. There is no individual, there is only the community." And a clone asserting his/her individuality is likely to be sentenced to exile — which is even worse than it sounds, as the Valley community is apparently all that is left of humanity.
- Literary Allusion Title: From Shakespeare's Sonnet 73.
- Mandatory Motherhood: If you are capable of conceiving and bearing children, you will, and as often as possible.
- Parental Abandonment: Mark never knew his father, and was only seven when his mother committed suicide.
- Scavenger World: The Valley community is dependent on salvaging supplies from the nearby cities, in order to maintain the technological base they need to survive as a society of clones.