New York
private detective Duncan "Mac" Maclain is blind, but he has keenly developed his other senses. Skilled in self-defense, he pursues his work with the help of his faithful
guide dog Friday and assistant Marty. Retired actress Norma Lawry, an old friend, comes seeking advice. Her headstrong 17-year-old stepdaughter Barbara, herself a promising actress, is enamored with her leading man Paul Gerente, a much older
Lothario. Paul, who once had been Norma's lover, has convinced Barbara that Norma actually wants him for herself and only has married her father Stephen for his money. Stephen has invented a secret weapon for the U.S.
war effort. Barbara arrives at Paul’s apartment and finds him dead, with Norma there. Norma insists she'd found him that way, but Barbara concludes that Norma has killed him and threatens to call the police unless she leaves Stephen. Norma then turns to Maclain, who goes to Paul's apartment with Friday and Marty, only to find both the body and the rug under it missing. Mac picks up a clue and barges into Norma's house, pretending to be her curmudgeonly "Uncle Mac". Hansen the butler is second in command of a German espionage ring, waiting for an opportunity to get the plans for Stephen’s secret weapon. Hansen had one of his henchmen kill Paul, whose affection for Barbara was beginning to limit his effectiveness. The spies' ringleader is Barbara's dramatic coach, Cheli Scott, who spends the night at the Lawry home and immediately suspects Mac is not what he seems. Stephen arrives home and Cheli threatens to have Norma’s face disfigured in Stephen's presence unless he surrenders the final step to his invention. Mac, under guard, is locked in the cellar and sends Friday for help. When Hansen is sent to kill him, Mac knocks out the light there to gain an advantage in the total darkness, then overpowers him. Marty and Friday return with the police, and Stephen and Norma leave for Washington. Barbara, however, remains cheerfully behind to paint the town with her new "Uncle Mac." ==Production==