During the Second World War, British intelligence secretly wired the cells and common rooms of Trent Park, a country house outside London used to hold captured German generals and officers. Hidden microphones recorded thousands of hours of unguarded conversation, and the film follows the historians piecing together what those transcripts contain: precise details on V-weapon programs, submarine tactics, and troop movements, but also officers describing mass shootings and camp atrocities in the same offhand tone they used for gossip. Interviews with researchers who spent years in the declassified archives sit alongside dramatized reconstructions of the listening rooms and the stenographers transcribing every word in real time. The film traces how this eavesdropping operation, run largely by German-Jewish refugees who had fled the Nazis themselves, fed directly into Allied military planning while also becoming some of the earliest hard evidence of the Holocaust from the perpetrators' own mouths. It is a story about what people will say when they believe no one is listening.