Madelene Burden seems an unlikely heroine.

The beautiful Danish wife of Adam, a distinguished British behavioral scientist, she is unobtrusive, acquiescent, and "nothing much really" according to her father. Spending each day like her last, she perfects her make-up and wanders the grounds of her colonialist in-laws' vast manor, not-so-slowly drinking herself numb off a homemade concoction of 99.6% ethyl alcohol and water.

Erasmus seems an unlikely romantic lead.

Weighing in at a hefty 300 pounds, he is hairy, lice-infested, and just so happens to be an ape. Victim of a botched animal-smuggling attempt, Erasmus is believed to be "a new and hitherto unknown mammal, an apparently highly intelligent anthropoid ape." Adam Burden and his calculating sister Andrea (who, ironically, heads up London's Animal Welfare Foundation) anticipate the opportunity of a lifetime by introducing this new species to the world. Certainly this will ensure Adam's appointment to the directorship of the New London Regent's Park Zoological Garden, soon to be the world's most powerful animal institution.

Seeing in Erasmus a kindred spirit, Madelene realizes that "she too was an ape, for, while she might well be able to leave this cage, and this house, she would not get very far before running up against the financial, social and marital barriers that circumscribed her life." Enlisting the aid of the still-befuddled smugglers, Madeline and Erasmus make a daring and dramatic escape over the balconies and rooftops of London to the Edenic rural game preserve of St. Francis Forest, where Madelene explores her "animal" side and Erasmus his "human." Over the course of the next few weeks the unlikely pair experience each other physically and mentally, eventually fall in love, and plot their next move.

Madelene and Erasmus can only keep the outside world at bay for so long. Towards the novel's conclusion, we learn that Erasmus has come to England with a purpose after all, and much like the scores of animal activists, zoologists, journalists, and police who are trying to hunt the couple down, he too has a hidden agenda – one which affects not only Erasmus and his "people" but Madelene, a society's conscience, and the entire human race as well.