A car factory in Isenau, somewhere in the GDR. It is the only major plant in the region, almost everyone works here, almost everyone knows each other. An accident occurs during a test drive. One driver is dead, another seriously injured. The investigation shows: sabotage. Klausner, master of the test workshop, feels part of the responsibility and seeks consolation from his daughter Herta. But Herta, secretary of the technical director, is inaccessible and distraught. Shortly thereafter, Klausner realizes that she is involved in the case. - The two State Security Service employees who are investigating the situation are initially helpless. When they finally track down the perpetrators, the intern Brückner, who plays detective, bursts in their way. At the last moment, immediately before fleeing to the west, the saboteurs can still be turned in.