When Ping sees Hanno at the zoo, he experiences mixed feelings of excitement and sadness. Hanno is an imposing African gorilla, large, black, and much stronger than a human. The idea of such a magnificent wild animal living in a cage, behind bars and locked doors, is difficult to accept. But then Hanno escapes from the zoo. A few days later, his footprints are seen near Green Knowe, the old house deep in the English countryside where Ping spends his holidays...