When artist Simon Dykes wakes after a late night of routine debauchery, he discovers that his world has changed beyond recognition. His girlfriend, Sarah, has turned into a chimpanzee. And, to Simon's appalled surprise, so has the rest of humanity. Simon, under the bizarre delusion that he is 'human', is confined to an emergency psychiatric ward. There he becomes of considerable interest to eminent psychologist and chimp, Dr Zack Busner. For with this fascinating case, Busner thinks may finally make his reputation as a truly great ape.