From The Perry Mason TV Show Book (Revised)
June Lockhart (Lassie, Lost In Space) plays Mona Stanton Harvey, principal stockholder in a publishing company run by her brother, Everett, and wife of a screwy sculptor who goes by the name of Hannibal Harvey.
Hannibal is being blackmailed. Trouble is, Mona is in Seattle and he can’t get at her bank account because the publishing company is being audited. So, he gets his even screwier model, Bonnie, to write a blackmail note to Mona’s brother. Predictably, Everett gets the money out of petty cash and sends it to Bonnie. In the meantime, Mona returns from Seattle, finds Bonnie's blackmail note, and decides to pay the model a visit. So does Hannibal. Without seeing each other, husband and wife both discover Bonnie’s dead body. Although it is Mona who’s arrested for murder, she’s afraid her husband is the real killer.
Tom Grossman points out that Mona Stanton Harvey is actually Everett Stanton’s niece not his sister.