Daniel Quinn's philosophical novel Ishmael: An Adventure of the Mind and Spirit opens with the narrator reading the newspaper and finding himself both disgruntled and intrigued by a personal advertisement. The ad indicates that a teacher is looking for a student interested in saving the world. For most of the narrator's early life, he had searched for such a teacher, and he's angry that only now is one looking for him. He's sure the ad is a hoax, but he goes to the indicated address, only to find an empty office space with a gorilla in one of the rooms, looking at him through a glass pane. The gorilla is able to speak with the narrator telepathically, and the narrator quickly realizes that this is the teacher he's been searching for.
The gorilla's name is Ishmael. He was caught in the jungles of Africa at a young age and has lived his life in captivity ever since. He started out in a zoo, then ended up in a traveling carnival, and finally was purchased by Walter Sokolow, with whom he learned to communicate telepathically. Through his telepathic connection, Ishmael was able to have Mr. Sokolow get him books and help him educate himself. Ishmael's primary investigation began with the issue of captivity but grew into a more comprehensive exploration of humanity and the shape of the world. Ishmael, having been apportioned part of Sokolow's estate after Walter's death, is mostly independent and lives his life in the city, trying to find students to help spread his teachings.
Ishmael and the narrator begin a series of meetings wherein Ishmael helps the narrator understand his cultural history. Ishmael divides humans into two groups: Leavers and Takers. Takers are members of the dominant culture, which sees humans as rulers of the world, whose destiny is to grow without check and dominate first the planet, then the universe, through technological innovations. Leavers are members of tribal cultures that live more simply, following the same basic rules that govern other populations on Earth. Ishmael helps the narrator see that while it may seem that Taker culture has outwitted the ecological rules that govern other life-forms, in many ways Taker culture is in freefall, doomed to crash once it has depleted the planet of its biological and environmental resources.
In addition to helping the narrator see the traits of Taker and Leaver cultures, Ishmael shows the narrator how various cultural myths have helped shape both cultures. One of the main myths he discusses is the story of Adam and Eve. Ishmael helps the narrator see that while Taker culture, through the dominance of Christianity, sees this myth as explaining its own creation, historically this myth was used by Leaver cultures to explain the expansion of Taker cultures. Leavers were trying to understand why Takers had turned to agriculture and were trying to force their way of life on the Leavers. Leavers used the myth to explain that it was because Takers had eaten of the Tree of the Knowledge of Good and Evil — the tree the gods must eat from in order to know who should live and die. Thus, the Takers were acting like the gods because they believed they'd gained the gods' knowledge, when in reality, such knowledge does not belong to any life-form on Earth.
Toward the end of their discussions, the narrator gets caught up with personal matters, forcing him to miss several days of meetings with Ishmael. When he finally returns to Ishmael's office, Ishmael is nowhere to be found. He tracks Ishmael down to a traveling carnival and visits him at night, so they can finish their lessons. The narrator comes up with a plan to rescue Ishmael from the circus by buying him from the circus's owner. By the time he gets the cash together, however, Ishmael has died from pneumonia. The narrator gathers up a few of Ishmael's remaining belongings and starts contemplating how he'll fulfill Ishmael's command to become a teacher himself and help other people see the problems with Taker culture and find a new way to live in balance with other life on the planet.