This is a story about the Cooke family, who raise a chimpanzee named Fern along with the narrator of the book, Rosemary up until they are both aged five. The father is a research scientist studying chimp behavior and they live in a farmhouse where they are assisted in taking care of Fern, as well as documenting her every move, by a team of graduate students. Mom and older brother Lowell make up the rest of the family. The story starts in the middle, when Rosemary is in college, about to see her older brother Lowell for the first time in years. Lowell has become something of a black sheep while advocating for animal rights. Most importantly Rosemary wants to find out from Lowell exactly what happened to Fern, who was taken away one day when Rosemary was a child. She suspects that the story he has told her about Fern being taken to a chimp colony is not true, but she has no idea of how bad the truth really is. Let us just say that mistakes were made and that Rosemary must make some tough choices when she finds out what really happened.
While the story tells a lot about chimpanzees and the work that has been done researching their behavior, it is also about a family, a brother, sisters, mom and dad, and how their lives unfold.