Newspaper reporter and amateur ham radio operator John Keefe, anxious for a scoop, plants a shortwave radio in the courtroom to eavesdrop on the grand jury's investigation into the brokerage house owned by Anthony Pelton and Thomas Reedy, which is allegedly dealing in fraudulent stocks. When the story breaks in the newspaper under John's byline, John's brother Michael, the assistant district attorney, is castigated by his boss. Nevertheless, John continues to jeopardize his brother's career and decides to infiltrate the brokerage house by posing as Avery, a wealthy young investor from the South. In a meeting at Pelton and Reedy's office, John leaves behind his briefcase, which has a microphone concealed in it. Soon afterward, Pelton, who has become squeamish over the grand jury investigation, decides to skip town. While emptying the safe, Pelton is accosted by a gun wielding young man, and in the ensuing skirmish, the gun discharges into John's briefcase. As the young man falls unconscious to the floor, Reedy enters and shoots Pelton. When the police arrive, the young man is charged with Pelton's murder and Mike is assigned to the case. Meanwhile, John, who has been fired for drunkenness, is told by his editor that he will be rehired if he uncovers the mystery killer. Posing as a priest, John visits the accused in prison, where the young man confesses that Pelton tried to blackmail his father. When Mike learns of his brother's duplicity, he orders his arrest, and John is brought before the grand jury to testify. For refusing to betray the young man's confidence, John is jailed for contempt. While in jail, John's friend brings him the briefcase, and when John sees the bullet hole, he realizes that the young man is innocent. Begging his brother for a chance to make amends, John is released and goes to Reedy's office, where he digs a bullet from the desk. At that moment, Reedy enters and orders John into his car at gunpoint. Using the radio hidden in his briefcase, John broadcasts his location in Morse code, and ham radio operators pick it up and radio for help. As the district attorney and grand jury listen in, a motorcade surrounds the car and Reedy shoots John. Reedy tries to escape, but is captured by the police, and John is taken to the hospital, where he is reinstated by the paper.