The lives of Ruth and Mark are transformed by nevermind magic that Ruth learned from her mother-magic that can undo what has been done and alter the shape of reality. They fall in love and marry in their early 20s during WWII. They split up, then meet forty years later and fall in love again. When they first meet, their on-again-off-again romance and the challenges of wartime America force them to grow up quickly. Their marriage falls apart when they lose their four-month-old son, Davey, during a transcontinental train trip. They blame one another and divorce. Then, separately, each of them invokes nevermind, finds Davey, and raises him. When they meet and fall in love for the second time, they realize they've been living in parallel worlds and need to bring those worlds together into a new reality.