The Peculiar Crimes Unit is disbanded, but a gruesome murder forces its eccentric detectives back together for one last case. Arthur Bryant and John May, once celebrated for solving London's most unusual crimes, find themselves without a unit after crossing their superiors. While Bryant retreats into his books, a murder discovered by a former colleague draws him back into action. The discovery of a headless corpse in a politically sensitive location, coupled with sightings of a mythical creature abducting women, convinces Bryant that this is a case worth pursuing. Reluctantly reunited with a skeleton crew in a makeshift office, they must solve the murder within a week, navigating a complex web of gangland crime, Slavic mythology, the Olympics, and high-level corruption, all while facing the possibility that this case could be their last.

The premise sets up a classic Bryant and May mystery, blending their signature eccentricities with a complex, multi-layered plot. The narrative appears to focus on the detectives' unique investigative methods and their struggle against both criminal elements and bureaucratic obstacles. The inclusion of mythological elements alongside contemporary crime suggests a rich, perhaps even fantastical, exploration of London's underbelly. Readers can anticipate a fast-paced investigation with a strong emphasis on the partnership between Bryant and May as they confront a case that pushes their limits.