Carabiniere Michele Falcetti arrives in Viterbo to replace Antonio Fait, killed a month earlier. A new case prevents Marshal Rocca from taking the exam for the passage of grade: Roberto, his youngest son, is taken hostage during a robbery in a supermarket and his colleague Banti is wounded in the shooting against the robbers. The marshal manages to find his son and have all the robbers arrested, but he has to give up the precious collaboration of brigadier Cacciapuoti: the latter, caught by a heart attack during the investigation, goes on leave for health reasons.