These Latter Days tells the story of Ruth Mason, the oldest daughter of a distinguished Mormon family in Salt Lake City. Faced with the bleak future of Mormon spinsters at the turn of the century, Ruth accepts the proposal of Samuel Douglass, a farmer from Idaho. She soon learns that she has made a mistake that will literally send her to hell. After bearing him five children, and with another on the way, Ruth leaves Samuel when he begins to have religious delusions and talks of taking a second wife and selling all they have worked for.

Living in a time when a woman is either "a wife, a widow, or a virgin", Ruth flees with her children to St. Elmo, California, where she tells the townspeople she is a widow. In despair after the birth of her sixth child, she gives up until the local physician, himself an outsider in a Mormon community because of his outspoken atheism, comes to her aid.