Susan Wheeler is a third-year medical student, the protagonist who single- mindedly jeopardizes her career, life and family's lives in order to explain why patients at Boston Memorial Hospital lapse into irreversible comas during minor surgery. She is also Robin Cook's vehicle for attempting to portray the medical world's hostile attitudes towards women in medicine.

She has a brief fling with her supervisor, Chief Resident Mark Bellows, whose wooden dialogue is as unconvincing as his insouciance when Susan explains that there has been an attempt on her life within the previous hour. Dr. Robert Harris, chief of anesthesia, is such a poorly contrived male chauvinist that he serves only as a parody of Cook's poor skills at characterization and dialogue. Consider this deprecation of Susan Wheeler: "'So you reverted to the vestiges of your sex,' said Harris condescendingly." Dr. Howard Stark, the chief of surgery, is the one character who is willing to listen to Susan's suspicions and hypotheses. This apparently sympathetic ear belies a conspirator who listens only so he can monitor her investigation and try to terminate it — a repeated pattern in Cook novels.

Indeed, Stark sends a thug to murder Susan Wheeler. When the job is botched, Stark lures her to his office, drugs her, and has her wheeled into the operating room — ostensibly for an emergency appendectomy; there he attempts to send Susan, too, into an irreversible coma.