When the body of a young woman is found in the city of Besźel, Inspector Tyador Borlú of the Extreme Crime Squad is called to investigate the murder alongside Officer Lizbyet Corwi. Although Detective Naustin presumes her murder can be easily explained, Borlú notices strange similarities to an old case.
The young woman's body was found at the Bulkyá Docks – an area known for its close overlap with the city of Ul Qoma. Although Ul Qoma and Besźel occupy the same geographical space, the cities have a dangerous and volatile relationship with each other, and citizens are trained from childhood to unsee everything in the other city. Commissar Gadlem thinks this is a case for Breach – the secret police who ruthlessly patrol all cross-border crime. Gadlem thinks someone else should take on the case, and that maybe it's too personal for Borlú… But Borlú insists he can handle it.

Borlú is interrogated by the Ul Qoman Militsya and is promptly taken to the Militsya HQ. He broke the terms of his agreement with Dhatt and she is furious – his possible deportation is out of her control. She's got him under constant surveillance. Dhatt knows this case means more to Borlú than being just another murder.