4 ideas
Tasio's twin brother Ignacio was the policeman who helped convict him. When identical killings resume just before Tasio's release from prison, profiler Unai 'Kraken' López de Ayala must decide whether the original conviction was wrong or whether someone is completing the pattern.
The killer's ritual encodes a sequence. Once investigators decode the signature, it becomes a forecasting tool: they can narrow the future victim pool and try to get ahead of the killer rather than only reacting to bodies.
The novel argues that an investigation run by people closely tied to the suspect, such as a twin brother, is vulnerable to motivated certainty. Once a conclusion carries personal weight, contrary evidence gets filtered out and the case hardens into accepted truth. The killer's closeness to the current investigation repeats this danger, turning insiders' access into the investigation's blind spot.
Kraken treats Vitoria's medieval landmarks, legends and archaeology as a text the killer is writing on. Because the killer chooses staging sites for their historical and symbolic meaning, understanding local heritage becomes as important as forensic evidence. Under this lens, a crime scene's location is a deliberate message, not a matter of convenience.