A 30-year-old missing persons case lands on Thiel's desk: after the disappearance of 15-year-old Sven, his parents received letters from an unknown Chris, who was supposedly travelling with their son. Now, new letters arrive from Chris.

Former detective Dennert - Ingo Thiel's old colleague and mentor - suddenly turns up at Mönchengladbach police headquarters. Dennert's visit has an important reason: there are new leads in a 30-year-old unsolved missing persons case. Back then, 15-year-old Sven disappeared one evening without a trace. The hastily assembled special commission was groping in the dark. It was all the more disturbing when letters from various countries soon arrived at the parents' home: all written by a boy called Chris. He wrote that Sven was doing well and that they were on a long journey. The letters were a real test for the parents' nerves. The police believed he was a freeloader because there was no Chris in Sven's circle. Then suddenly there were no more letters. For 30 years. When the now 70-year-old parents receive letters from Chris again one day, it hits them hard. Could there still be hope of finding their son? Now the mysterious new letters land on Ingo Thiel's desk. He orders an intensive forensic examination of the evidence. An expert in operational case analysis, specially appointed by the LKA, confirms that not only is the style of the new letters similar to the decades-old copies, but the sentence structure and choice of words have also remained at the level of a teenager with a low level of education. This circumstance seems strange to the investigators .