Inspector Tyador Borlú is an experienced detective with the Extreme Crime Squad in Besźel. An unmarried and relatively solitary man, he centers his life around law enforcement, relying on a deep understanding of urban geography and criminal behavior to solve cases. He possesses an open mind that allows him to consider highly unlikely possibilities when presented with bizarre evidence.

Senior Detective Qussim Dhatt is an experienced investigator for the Ul Qoman police force. Territorial and prone to using physical intimidation during interrogations, he works to establish his authority on his home turf. Despite his initial reluctance to collaborate across city lines, he shares a common dedication to police work and solving homicides.

Mahalia Geary is a highly intelligent Ph.D. student in archaeology who conducts research at an excavation site in Ul Qoma. Known for her controversial theories, she is intensely curious and unafraid to challenge the established academic consensus. Her unorthodox academic interests draw her into political circles and place her at the center of dangerous urban myths.

Constable Lizbyet Corwi is a local Besźel police officer who assists Borlú with his homicide investigation. She is highly observant, noticing immediately that the murder victim's makeup does not match the profile of a typical sex worker. She proves to be a loyal, efficient, and dependable subordinate who handles difficult logistical assignments with ease.

Yolanda Rodriguez is a graduate student studying in Ul Qoma and the closest friend of Mahalia Geary. Her disappearance shortly after her friend's murder raises serious alarms for the investigating detectives. Like Mahalia, she studies history and archaeology, maintaining a deep fear of the dangerous forces rumored to operate between the cities.

David Bowden is an academic and the author of *Between the City and the City*, a controversial and officially debunked book about a mythical third city called Orciny. Disgraced within the mainstream academic community, he lives quietly in a cluttered apartment. He maintains a fascination with ancient artifacts and the forbidden history of the divided cities.

Ashil is an overseer and operative for Breach, the mysterious and deeply feared entity responsible for maintaining the rigid separation between Besźel and Ul Qoma. Operating with authority that supersedes local law enforcement, he maintains an intimidating presence while enforcing the strict borders separating the populations.

Isabelle Nancy is Mahalia Geary's academic adviser. A mainstream scholar, she frequently bemoans her student's misguided obsession with debunked folklore, warning that such interests threaten professional credibility. She escorts investigators around the dig site to explain standard archaeological theories.

Commissar Gadlem is Borlú's superior officer in the Extreme Crime Squad. He manages the political fallout of high-profile cases and assigns Borlú to continue his investigation as a consultant across the border when standard procedures fail.

Mr. Geary is Mahalia's grieving American father. Unfamiliar with the strict protocols separating the two cities, his desperate desire for justice drives him to flout border rules to investigate the political extremists he blames for his daughter's death.

Mrs. Geary is Mahalia's mother. While grieving, she manages to supply Borlú with crucial information regarding the far-right groups her daughter had angered, assisting the investigation before facing deportation.

Pall Drodin is the leader of the local chapter of the Besźqoma Solidarity Front, a unificationist group seeking to merge the two cities. He provides Borlú with information about Mahalia's activities within radical political circles.

Mikhel Buric is a liberal politician involved in the complex political ecosystems of the twin cities. Though he publicly maintains mainstream political views, his private ambitions tie him to wealthy multi-national corporations and underground operations.

Mikyael Khurusch is a man with a prior criminal record whose van was used to transport Mahalia Geary's body across the border. He claims the vehicle was stolen and maintains a solid alibi, though Borlú suspects he deliberately left his cross-border visa inside for a price.

Shukman is the forensic pathologist for the Besźel police force. He provides Borlú with essential medical details regarding the victims, including the specific timing and nature of the injuries sustained before death.

Aikam Tsueh is a security guard working at the archaeological excavation site. He draws the detectives' suspicion after correctly identifying a mail bomb despite lacking formal training in explosives, and later serves as a courier in the search for missing students.

Jaris is a member of a unificationist political faction. Fearing for his own life after Mahalia's murder, he reaches out to law enforcement with fragmented information about mythical cities before fleeing into hiding.