Rhoda Reynolds has just married Carl Reynolds who is the son of a wealthy man, Philip Reynolds (John Hoyt), who despises her, probably because this marriage was the first time Carl stepped out from the shadow of dad and thought for himself.
Rhoda has been paying blackmail money to her first husband whom she never divorced because she had been told he was dead. It's clear this guy is not going away until he bleeds her dry. One night in the middle of the night Rhoda goes to let her first husband know she can't get the money he wants now. He threatens to take a family heirloom off of her finger in payment. The scene switches to a neighboring apartment where the scuffle wakes the resident who calls the police. When the police arrive, they find Rhoda's first husband, Arthur Kaine, has been murdered. They quickly trace things back to Rhoda and she is arrested for the murder. Perry is on the case.
Considerable time is spent on some games that Perry Mason plays with a doorbell to the victim's apartment. Specifically, he muddies the water as to whether it was a buzzer or a bell, and if it was a bell, was what was heard in fact an alarm clock? None of this clears Rhoda of guilt, but it does cast doubt on how reliable a crucial prosecution witness is, which infuriates D. A. Hamilton Berger.
I'm not sure why Berger tried Rhoda for first degree murder rather than second, degree because any sentencing portion of the trial would definitely show the victim up as an unconscionable liar and blackmailer who was constantly menacing Rhoda, probably winning her the sympathy of the jury.
This same Perry Mason mystery was made into a movie in 1935 by Warner Brothers and directed by Michael Curtiz. It is interesting to compare Warren Williams' light-hearted interpretation of the role of Perry Mason versus Raymond Burr's more dramatic presentation. That film had Erroll Flynn in his second American film in a bit part as a corpse.