An unnamed detective is hired to find his client’s husband. The husband is a salesman who disappeared at the corner of a street near their home, and the client's brother has tried without success to find him.
The detective never seems to be quite certain what he is looking for, and the story reads often as though he has two and two in his two hands, but he cannot make them make four. He seems to be in between very distinct places for much of the book: the couple's apartment and his own office, the office and the dry channel where the prostitutes work, the office and the noodle-shop, and so on. Neither the places nor his journeys between them lead to any advancement in his case, as though the eponymous ruined map he has been given keeps him in the wrong place, rather than guiding him to where he might find answers.
In the same way, the detective seems to be in-between the pages of the book, but never quite in, let alone driving, the story. He expects to find ways of resolving the mystery through his obsessive attention to irrelevant details, like traffic patterns or matchbooks. He never seems to get any closer to the object of his search, except insofar as he begins to identify strongly with the husband, thereby failing to find either of them.
The Ruined Map is written in a naturalistic way, and is bleakly funny in places, but both characteristics serve to underline isolation as a fundamental human experience, as the detailed description of particular places throws into relief the universality of absurdity as characteristic of life.