De Luca is killed by Marchetti's chauffeur. Marchetti ordered the murder because he was to be accused by De Luca. The two have a car accident while going home to get an alibi. There is a witness, Sironi, who calls the police. But when the police arrive the car has gone and so have the two men. Inspector Santi and young judge Novelli look into the strange case. Marchetti, however, is a powerful man and Sironi and his family begin to be obsessed first by threats then by assaults.

Una noche Giorgio Sironi, un joven doctor, conduciendo hacia su casa es testigo de un terrible accidente de coche. El conductor de uno de los coches está gravemente herido y Sironi trata de ayudarle. Llama a una ambulancia e informa a la policía, pero sin saberlo, es alcanzado por un círculo maligno. En esta película llena de acción todo se convierte en una pesadilla y la desesperada lucha por la vida y la libertad.