In New York City, in the middle of the night, a shriek sounds as a body falls from the Harker Apartments to the pavement below. Inspector Russell and his bumbling assistant Wilfred interrogate the secretary and maid of the dead man, Mr. Harker. The secretary is really reporter Pat Morgan, who three weeks earlier, was planted at the apartment to investigate a possible connection between Harker and racketeer Joe Martini, who also lives in the apartment house. Among Harker's letters, Pat finds a card with a serpent's insignia and the words, "You Will Hear It." Rival reporter Ted Rand, whose marriage proposals Pat has rejected, sneaks into the apartment, and when Pat calls in her story, he picks up another phone and impersonates a rewrite man from her paper. Ted gets the story for his own paper, and because of this, Pat is fired the next day. Also, the next day, Bee Covey, who lived beneath Harker, is found dead in her apartment, where another serpent card is found. The police believe that the dead woman's husband killed both her and Harker after learning that they were having an affair, but when Covey is found dead in the East River, that theory is discredited. To get back at Ted, Pat gives him a phony story that the janitor killed Harker. Ted, however, calls this story in to Pat's paper so that she will get back her job back, and when she learns what he has done, they frantically call the paper back. Harker's maid shows Pat a letter she found hidden, which threatens those responsible for framing Denny Fagan, who died in the electric chair. Pat then pays Peterson, the janitor, ten dollars to let her into Martini's apartment for a few minutes. Martini sees her leave, after which she calls Ted to tell him about the Denny Fagan connection. When they hear someone else on the line, Ted comes over to spend the night. As Ted apprehends Martini intruding, they hear another shriek and find that a police investigator who had been searching through Martini's papers, was killed by someone who thought he was Martini. After Martini is arrested for six other gang killings, Pat receives a serpent card in the mail. She then goes with Peterson to the cellar to pick out her trunk, and he knocks her out and puts her into the incinerator. He is about to light it when Russell and others get him to unlock Martini's apartment. Wilfred notices Peterson's nervousness and follows him to the cellar. They struggle and Pat escapes, and when Russell and the others arrive, they are astonished to find that Wilfred has subdued Peterson. Later, Ted visits Pat, who is recuperating, and relates the story: Peterson was the brother of Denny Fagan, an innocent cab driver who was framed for murder by Harker and Martini. After he killed Harker, Peterson killed Mrs. Covey to throw suspicion on her husband, to whom he sent a note implying that his wife was having an affair with Harker, but Covey, believing the note, committed suicide. Peterson killed all his victims with gas, and this explains the card sent to the victim, with the serpent insignia and the message "You Will Hear It," which referred to the hissing sound of the deadly gas in the pipes. When Pat's editor calls to ask her back, Ted objects to his future wife working and, after borrowing three dollars for a marriage license from the maid, embraces Pat.