Thelma Brent arrives at the murder scene in a 1958 Sunbeam Rapier convertible.
Has a convoluted family situation. Clinton Forbes married his ex-wife's brother's ex-wife (Polly). That means Polly was Clinton's wife and ex-sister-in-law and Clinton was Polly's husband and ex-brother-in-law.
An unusual situation for Perry Mason, as the murderer kills 3 separate people at 3 different times.