The biologist is the main protagonist and first-person narrator of the novel. She has qualified for the 12th expedition into Area X by way of her expertise in transitional environments. Her husband was a member of the 11th expedition; he died of cancer six months after his return. The biologist is an acute observer of natural phenomena; she is inquisitive, solitary, independent, and brave. Early in the novel, the spores of a mysterious organism contaminate her. She is the only member of the expedition who is immune to the psychologist’s hypnotic suggestions. The biologist is drawn to the natural habitat of Area X, and at the end of the novel, her decision to stay there rather than rejoin the world of cities reveals her preference for nature—and perhaps that, as a result of having inhaled the spores, she is merging with her natural surroundings.

The psychologist is the leader of the 12th expedition. She is capable of controlling the other members of the expedition through hypnotic suggestion. After the anthropologist’s body is found in the tunnel, the biologist becomes suspicious of the psychologist’s motives and behavior, yet the biologist comes to realize that she also depends on the psychologist to continue leading the expedition.