Half brothers Adam and Charles Trask share a mysterious devotion, as well as an intense rivalry. When the lovely but immoral Cathy Ames enters their lives. Adam mistakes her beauty for goodness and marries her. But Cathy soon commits adultery with Charles, bears twin sons, and eventually deserts husband, children and lover to take up residence in a brothel. The twin boys grow up believing their mother had died in childbirth. Like their father and uncle, Caleb and Aaron compete with and depend on each other. Caleb falls in love with Aaron's fiancee, but desperately tries to suppress his feelings. Then on the ever of World War I, Caleb discovers the truth about their mother. At first he wants to protect the weaker Aaron from this knowledge, but later, in anger, Caleb uses it as a weapon against his brother. In the end - like the Bible's Cain who is his spiritual progenitor - Caleb must travel an awful path of retribution, and possible atonement, for his evil.