Sauerland, in the fall of 1995: A walker finds the body of high school graduate Sonja Risse on the Wilzenberg. The fact that the murderer leaves a music box with the lullaby "Hush Little Baby" at the scene does not solve the problem. In Cologne 25 years later the investigative journalist Stefanie "Mütze" Schneider made a surprising discovery: In a disused parking garage she was filming a stripped male corpse - next to which a music box was running. When her colleague Jan Römer, who reported on the spectacular Sonja case in 1995 as a young journalist, recognizes the melody from back then, he immediately believes there is a connection. He and his ambitious colleague drove to Wilzenberg to interview Sonja's mother Maria, her former teacher Waldheim and her best friends. The more the journalists collect, the clearer the contradictions and gaps that the investigators should have noticed at the time. In the meantime, more people have arrived in the Sauerland: The Office for the Protection of the Constitution Münch is looking for Thomas Sonnefeld, who has returned after 25 years abroad. The two men share a dangerous secret that reporters uncover.—ARD Das Erste