New York detective Duncan Maclain (Edward Arnold) refuses to allow blindness to interfere with his work, which is aided by his faithful dog Friday, his butler, Alistair (Mantan Moreland), and his assistant, Marty (Allen Jenkins). One day, actress Norma Lawry (Ann Harding), an old friend, visits Mac and asks him to help her prevent her stepdaughter Barbara (Donna Reed) from doing something foolish with actor Paul Gerente (John Emery). Paul, a cad who had once been Norma's lover, has convinced Barbara that Norma only married her father Stephen (Reginald Denny) for his money. Mac initially tells Norma that she doesn't need a gumshoe and suggests that she talk to Paul herself, but the plot soon thickens when the government project Stephen is working on attracts Nazi spies. In the end, Mac deals with both the personal and political intrigue like a true professional.