When "Diamond" Ed Barnaby (an uncredited Walter Baldwin) is paroled, he sets out to give $100,000 worth of diamonds to his daughter, Betty (Ann Savage (actress)). Aware that several shady characters know he has the jewels, he stashes them in a safe deposit box in the Arcade Building. Betty later receives a call asking her to meet him there, but he never shows up. She contacts her father's only real friend: Horatio Black, better known as Boston Blackie. He agrees to help and drops Betty off at the apartment of his wealthy friend, Arthur Manleder (Lloyd Corrigan), for safekeeping. His sidekick, "the Runt" (George E. Stone), has to postpone his wedding to statuesque bubble dancer Dixy Rose Blossom (Jan Buckingham).