From The Perry Mason TV Show Book
Actress Constance Ford plays a dual role of sorts as a troubled woman living a double life. Helen Reed, a mild-mannered housewife by day, turns into Joyce Martel, a roaring harlot by night. Perry needs Joyce Martel's testimony to clear her brother of a murder rap. Helen Reed informs Perry that she can only recall her other half, Joyce, when her psychiatrist puts her under hypnosis.

A dramatic courtroom drama ensues, with Helen Reed turning into her double on the witness stand.
+ It seems to me that the characterization of Joyce Martel as "a roaring harlot by night" is not accurate; she definitely enjoys her nightlife but nothing in the episode would substantiate "harlot", much less a "roaring" one.