In "Fortitude" Dr. Elbert Little, a Vermont family physician, visits the laboratory of Dr. Frankenstein and his trusty assistant, Dr. Tom Swift. Frankenstein has only one patient, Sylvia Lovejoy. His life work has been to keep Lovejoy alive. In 78 operations over the last 36 years, Frankenstein has replaced every one of her organs with prosthetic devices, so that now she consists of a head on a tripod, attached by tubes to various machines.

Frankenstein controls her mood, as he controls all her functions, from a "fantastically complicated" master console. Usually he makes sure that she feels joyful and loving, but last month a transistor went bad in one of the machines and she felt depressed for a while; so depressed, in fact, that she wrote to Dr. Little and asked him to bring her some cyanide.

Lovejoy's only friend is Gloria, the beautician who comes every day to care for her hair. Gloria is horrified over what Sylvia Lovejoy has become; she sees only a "spark" of the real person remaining, but she knows that the "spark" wants to die. After Frankenstein fires Gloria for speaking about death in Sylvia's presence, she sneaks back into the room when Sylvia is sleeping and puts a loaded revolver in her knitting bag.

Later, Sylvia finds the gun and tries to kill herself, but her prosthetic arms have been designed not to allow her to do that. Instead, she shoots Frankenstein, who promptly becomes the second head attached to the machines. (It seems he has designed all the prosthetic organs to be able to serve two "persons," so that he and Sylvia will be able to "live in such perfect harmony . . . that the gods themselves will tear out their hair in envy!")