The philosophy student Kovrin is on the verge of a nervous breakdown. His doctor suggests a rest in the country and so Kovrin decides to visit his childhood friend Tanya Pesotsky on her father's estate. While there he tells Tanya the legend of the black monk: a desert monk whose image has been reflected in mirages for a thousand years and who will soon return in the flesh.

One day in the garden, the black monk appears to the young man. This gives him joy and energy, even though he realizes that it is a hallucination. "What harm is in it?" Kovrin asks himself. As the summer goes on, the black monk continues to visit. Kovrin asks Tanya to marry him, they wed and move to the city. At one point Kovrin's hallucinations and disordered thinking overwhelm him; he agrees to medical treatment which evidently cures his mental disorder. Yet, his feelings of energy and creativity also disappear, along with the black monk.

Kovrin realizes that he hates his wife and she hates him. She returns to her father and his beloved garden, while Kovrin receives a professorship, a position he never actually takes because he is too ill--he has begun to hemorrhage from the lungs. Soon after receiving news of his father-in-law's death, he sees the black monk again and dies of a hemorrhage.