In "Dark Inheritance", a wealthy geneticist has asked a number of U.S. scientists to raise bonobos chimps in their homes -- supposedly to study their reactions to an enriched intellectual environment. Umber is one such young chimpanzee. Placed with Dr. Jim Dutton, an anthropology professor at Colorado State University, she has become much more than a project animal. Dutton can't help but notice the startling differences between Umber and any other chimp he has ever known. As the years pass, she acquires a huge vocabulary in sign language; she can use a computer, tools, and kitchen appliances; she becomes almost a sister to Dutton's daughter, Brett.

Other experimental chimps are being raised elsewhere in the U.S., and Dutton compares notes with their scientist "hosts". All the bonobos are brilliant. What was done to them before they reached the U.S. -- and how have they been altered -- and why? It is not until the chimps' owners start recalling their animals that Dutton is galvanized to discover the truth.