A master of arts named Andrei Kovrin has strained his nerves and been advised to take a vacation by his doctor. After spending three weeks on his own estate, Kovrin decides to visit his former guardian Yegor Pesotsky, a renowned horticulturist. When he arrives at Pesotsky's home, Kovrin finds the old man and his daughter Tania worried about a coming frost. Kovrin sits up all night with Tania to watch over the plants and learns how much Yegor values his orchard. Over the course of the summer, the two young people grow close, and Kovrin describes his physical state of happiness as if "every vein in his body was quivering and fluttering with pleasure."
Kovrin is restless and does not sleep much, but he talks a great deal and drinks a lot of wine. One evening, he clasps Tania's arm and tells her of a legend that has been preoccupying him. It is about a monk dressed in black, who wandered in the desert 1,000 years ago and set off a series of mirages so that it seemed as if his image was seen walking in different countries all over the world. The crux of the legend is that 1,000 years after the day the monk walked, his mirage will return to earth and "reappear to men." After saying this, Kovrin leaves to walk by himself in the garden and catches sight of a tall black column like a "whirlwind" racing towards him. As it approaches, he realizes that it is the monk. Although the apparition does not say anything, Kovrin is faintly perturbed by the man's pale face and "sly smile." Upon returning to the house, Yegor and Tania remark how "radiant and inspired" Kovrin looks, although Kovrin decides not to tell them what he has seen.
After supper, old Yegor comes to Kovrin's room and gently encourages him to marry his daughter. Pesotsky explains his great love for the "business," and particularly for the orchard, which he insists will go to ruin if anyone other than Kovrin weds Tania. The next day, Kovrin mediates a quarrel between Pesotsky and Tania, and again Kovrin sees the black monk in the garden. The monk tells Kovrin that he is one of God's elect and warns him that the accompanying traits of "exaltation, enthusiasm, ecstasy" will not ensure his physical health. When Kovrin asks the monk whether he is mad and if this is an illusion, the apparition replies that he is not and that it is real. Kovrin is now assured of his own "loftiness" and decides to marry Tania. He meets the monk several times week while walking around Pesotsky's estate.
Pesotsky arranges a lavish wedding for the young couple. The action switches to Kovrin's townhouse where he is reading in bed. Tania awakes to find her husband talking to the monk and concludes that he is mentally ill. Kovrin is treated for megalomania and once again returns to spend the summer with Pesotsky. Unfortunately, the protagonist treats the old man with disrespect and rudeness, and Tania realizes that there is something "ugly and unpleasant" in her husband's face that was not there before.
Kovrin accepts a professorship at the university but cannot deliver his first lecture because he is too sick. He is now living with a woman other than Tania and is coughing blood due to a hemorrhage in his throat. While visiting the town of Yalta, the protagonist receives a letter from Tania blaming him for her father's death, which has resulted in the orchard's destruction. The protagonist remembers how spiteful he was to Yegor and Tania, and Kovrin experiences an emotion "akin to terror." While he is thinking on the past, Kovrin hears the sound of violins playing and feels "a thrill of sweet, exquisite delight" wash over him. The monk appears and berates Kovrin for thinking that he was deranged and not believing that he was a genius. Kovrin starts to hemorrhage heavily from his throat and dies calling Tania's name, while the monk whispers to him that his body can "no longer serve as the mortal garb of genius."
The Black Monk was written in the summer of 1893 and published in January 1894. It thus predates many of Chekhov's later tales dealing with "nerves" and mental health, such as On Official Duty. However, as opposed to the later story where the central character's "nerves" are symptomatic of his troubled conscience and social aspirations, this tale introduces a protagonist who thinks madness validates his own genius. In this tale, Donald Rayfield notes that Chekhov "deals with insanity as inspiration" and that he "subtly combines the symptoms of mental derangement with those of physical illness." It is difficult for readers to determine if Kovrin is killed by tuberculosis or destroyed by his own lunacy.