John Irving's 1968 novel was published early in his career, in 1968 when he was still in his twenties. Its structure is unusual in that it has dual protagonists for part of the novel, Graff and Siggy.

Hannes Graff is an Austrian college student studying in Vienna. Siegfried Javotnik, known as Siggy, is also a college student studying in Vienna. The two young men drop out of university and hatch a plan to release the all of the animals from the Heitzinger Zoo. Gallen von St. Leonhard is a young woman traveling on her own through Europe, and Graff takes up with her after Siggy's untimely death in a motorcycle accident. Keff is the driver of the truck hauling beehives that Siggy crashes into, causing his death when the bees attack him.

A section of the novel reveals the history of Siggy's family. While they do not interact with Hannes Graff or Siggy, the characters come alive as a backstory that Siggy narrates. Included and prominent is Vratno Javotnik, the father of Siggy. Vratno makes his way, during his efforts to avoid World War II, from his home in Yugoslavia to Vienna, where he meets the woman who will become Siggy's mother.

Vratno's misadventures bring him into contact with menacing Slivnica family: Todor, its leader, and Bijelo, the oldest son. Lutvo and Gavro are half-wit twins, and other siblings are Julka, Baba, and the beautiful Dabrinka.

The Marter family includes Hilke, who is Siggy's mother. She exits his life in childhood. Grandmother and Grandfather Marter are Hilke's parents. Zahn Glanz is the boyfriend of Hilke before the war.

Gottlub Wut is the leader of Motorcycle Unit Balkan Four while Yugoslavia is occupied; he helps Vratno hide during the war. Ernst Watzek-Trummer is the man who becomes the stand-in father for Siggy after his grandfather's death and his mother's exit from his life.

O. Schrutt is a sadistic watchman at the zoo who works the overnight shift; he is overpowered by Hannes and Gallen on the day of liberation.