Amanda and Mathilda are two sisters who live in rural Wisconsin; they are very close, but very different. While Mathilda is petite, well-liked, pretty, and adventurous, Amanda is tall, clumsy, awkward, and serious. When Mathilda marries Carl, Amanda feels betrayed and leaves to go to nursing school. She dives into her work and makes her entire life about helping the sick and injured. Meanwhile, Mathilda and Carl are married and living together on a small island just away from the family farm. They are happy there, and welcome their child, Ruth, into the world. A short time later, however, Carl begins to feel trapped, enlists in the army and is sent away to France. Mathilda is devastated and angry at his departure. She moves back to the mainland and into the old house of her late parents.
Amanda begins to feel agitated and upset. She's also sick all the time, and a nervous wreck. She is persuaded to take a rest, and travels back to the family farm to stay with her sister and niece. The three grow very close, and Amanda begins to see Ruth as their child, becoming very protective of her. After living in the farm house for a while, Amanda persuades Mathilda to move out to the island. At first, the idea does not go over well, but Mathilda soon agrees, and the three of them move out to the island.
During the summer, it becomes apparent that Amanda is pregnant and desperate to hide it from everyone. Mathilda agrees to adopt the child as her own and make up a story about the baby being an orphan from a "hired girl." Amanda is pleased with this arrangement, but still must hide her pregnancy, so she does not leave the island until the baby is born. When the baby finally comes, Mathilda delivers it in the house with Ruth under the bed. Sometime in the night, Amanda changes her mind about Mathilda raising the baby and tries to leave the island by walking across the ice with the child.
Ruth, who is approximately four at this time, follows Amanda out onto the ice because she doesn't want her to leave. Mathilda runs out after them, trying to get Ruth back and find out why Amanda is leaving. Out on the ice, they walk over a thin patch and the ice starts to break. Ruth and Mathilda go under, while Amanda desperately tries to save them. Mathilda pushes Ruth to the surface to save her, but falls back in herself. Amanda tries desperately to pull her out, but can't do it without falling in, so Mathilda bites her sister's finger to force her to let go and leave her to drown in the freezing water. Ruth is half dead and frozen on the ice with the baby, but she is revived.
Amanda takes the new baby to a woman in town who has recently had a stillborn child. She tells the woman that a hired girl had the baby and then died in childbirth. She also tells her that the baby's name is Imogene. The woman is so taken with the child, and so amazed at the situation that she doesn't notice that both Ruth and Amanda are frozen and wearing nightgowns. She also doesn't notice the blood on Amanda.
Soon after Mathilda's death, Carl returns home from the war with serious injuries, and is nursed back to health by Amanda. Ruth, traumatized, is behaving oddly and very leery of her father, whom she barely knows. The three of them live together for a while without incident, but after a while, Carl starts to suspect that there might be more to the story of his wife's death than he has been told. As far as he knows, his wife wandered out into the night all alone and disappeared, later to be found under the ice.
Amanda starts having serious issues again with her nerves and anxiety. She is institutionalized in a mental hospital, and Carl is left to take care of Ruth on his own. Worried that he doesn't know enough about children, he asks his cousin, Hilda, to come to the farm and care for Ruth. Ruth dislikes Hilda almost instantly. She is strict, serious, and humorless. She sees Ruth as a problem child, and seems almost to enjoy punishing her.
Later on, Ruth and Imogene become friends.