When Dario Argento directs his second film and Ennio Morricone puts the soundtrack the result shall be just great. This is another 'Giallo' mystery film about a series of murders connected to a pharmaceutical company. Franco Arno is an interesting character. Although he is blind he used to be an active journalist and now he makes a living writing crossword puzzles. He lives with his young niece Lory and one night as they return home, he overhears a weird conversation that troubles him. Soon murders that have to mess with people who work at the company make him believe that something strange happens and he decides to investigate it with the help of reporter Carlo Giordani. The cinematography and suspense are at high levels and Karl Malden gives a good performance as a blind man.