The Marsh is a novella presented as the first person narrative of a young, male unnamed narrator. The story opens with a dream made up of the narrator's memories of bathing, when he was a boy, in Isfahan's Zayandehrud river, in company with his father and his father's friends. We then see the narrator living in Tehran as a young man with two friends, Khashayar an unpublished poet, and Hamid whose main concern is to find himself a suitable wife.

But it is the narrator, not Hamid, who marries; his bride is a cousin with whom he has long imagined himself to be in love. The two marry after the death of the narrator's father, who owned a small tailoring business in Isfahan. Gradually the narrator becomes alienated from daily life, and lives out an obsessive imaginary relationship with his dead father.

As the novel proceeds we see him withdraw from his wife and her family, as well as from his former friends and job in Tehran, until he - and the reader - are quite unable to distinguish reality from hallucinatory fantasy.