A detective story set in two cities that occupy the same geographical space. Besźel and Ul Quoma have different laws, languages, faiths, and traditions, and their citizens learn from birth to maintain the delineation between the two cities by carefully ignoring the people and scenery of their sister city while interacting only with their own, lest they be taken away by a strange secret police. Against this backdrop, a detective investigates the murder of a young woman and discovers clues that lead him to both cities and something bizarre happening between them.