Qussim Dhatt is a police officer from Ul Qoma who works with Borlú on the case; while initially territorial, he becomes a collaborative partner in the investigation.

Lizbyet Corwi is a regional constable who aids Borlú with her keen observation and reliable nature, proving invaluable in moving the investigation forward.

Mahalia Geary is a brilliant Ph.D. student whose mysterious murder acts as the catalyst for the story's events.

Yolanda Rodriguez is Geary’s closest friend, whose involvement in the storyline adds depth to Geary's character and aids in developing the plot.

David Bowden is a disgraced academic whose involvement in the case reveals the layers of complexity beneath the surface of the investigation.