World War Two blackouts turned London and Berlin into cities without streetlights, and this film follows the detectives who had to hunt killers using that darkness as camouflage. In London, the case centers on Gordon Cummins, the RAF airman dubbed the Blackout Ripper, who murdered several women in a matter of days before a dropped gas mask case tied him to the scenes. In Berlin, the parallel investigation covers Paul Ogorzow, the S-Bahn railway worker who attacked women walking home from night shifts, exploiting both the curfew and his own Nazi party membership to move without suspicion. Archival photographs, period newsreel, and location footage of the two capitals reconstruct how wartime conditions, mandatory darkness, fear of air raids, stretched police thin and gave both men their opening. Historians walk through the forensic work, still primitive by modern standards, that eventually closed each case. The film keeps its focus tight on method and investigation rather than spectacle, tracking how two very different cities caught two very different killers using the same wartime cover.