New York private detective Duncan"Mac" MacLain is blind but has keenly developed all his other senses. He pursues his work assisted by his faithful guide dog Friday, his butler, Alistair, and his assistant, Marty. Retired actress Norma Lawry, an old friend, comes to Mac seeking advice. Her headstrong 17-year-old step-daughter Barbara, herself a promising actress, is enamored with her leading man in a small theater production, the much older Lothario Paul Gerente. Paul, who had once been Norma's lover, has convinced Barbara that Norma actually wants Paul for herself and has only married her father Stephen for his money. At Mac's urging, Norma tried to reason with Paul, but he insists that he loves Barbara and laughs her off. Barbara is equally disdainful of her and agrees to meet Paul for dinner that night at his apartment. Norma's husband Stephen Lawry is a scientist leaving that night on a trip to test a secret invention on which he has been working for the government and the war effort. Worried about Barbara, she uses a pretext not to accompany Stephen and goes to the apartment. When Barbara arrives, she finds Paul's dead body and thinks that Norma has killed him, even though No…