This is the fictional journal of four months in the life of Doctor Tyko Glas, a turn-of-the century Swedish physician, who writes, "How can it have come about that, out of all possible trades, I should have chosen the one which suits me least?" Though Doctor Glas is over 30 years old, he has "never been near a woman." In fact, he finds the physical aspects of sexual intercourse rather repulsive. Even more repulsive is his patient Rev. Gregorius, a nasty 57-year-old minister who happens to have a lovely young wife.

One day Mrs. Gregorius, also his patient, presents Doctor Glas with a strange request. Her husband's sexual advances have become onerous to her. Could the doctor tell him that she suffers from a pelvic disease and, therefore, must avoid sexual relations for several months? Doctor Glas agrees to do so, but the Rev. Gregorius is not easily put off. He believes that God has given married couples the duty to procreate, so sex is not simply a question of pleasure or preference. It is a question of duty. Thus, he rapes his wife, believing that their sacred marital duty is more important than her health.

Meanwhile, Mrs. Gregorius admits (to the doctor) that she has fallen in love with someone else, a handsome young businessman. As the summer progresses, it is clear that Doctor Glas has fallen in love with his patient, a love that is as tortured as it is silent and unrequited. Eventually Glas becomes convinced that he must save his patient from her repulsive husband's advances by murdering him.

Thus, the doctor carefully plans to poison the minister, using cyanide pills that he had once prepared for his own suicide. His plan is successful. The minister dies of an apparent "heart attack." Unfortunately, at around that time the handsome lover announces his engagement to another woman. The bereft Mrs. Gregorius, who sees nothing in the doctor, is left alone. Doctor Glas is also alone. "Life has passed me by," he ruminates.