The fictional book is a sex manual, much like The Joy of Sex. It was written by the parents and is full of detailed illustrations of them engaged in numerous sexual positions. One day while the parents are out, the children discover it and their lives are changed forever. The story looks at the effect the book has on their lives over the course of many decades, jumping forward decade by decade. For example, it looks at the effect it has on the child at 10, then when they are 20 and so on.
The author tells the story by switching among the different points of view of the members of the family. The parents are unaware the children have discovered the book, so their story is very different from the children's. It also explores how each character feels about the others. For example, the husband thinks his wife is the most sexually desirable woman to him on the Earth and feels he is the luckiest man alive. On the other hand, she feels her husband is too mechanical when it comes to lovemaking, approaching it as some sort of scientific experiment.