The last episode broadcast to have been based on a novel by Erle Stanley Gardner.
Peggy/Ethel looks up Perry Mason's phone number in a Los Angeles phone book. His number is MA 5-1190.
This is based on the same premise as the season two show "The Case of the Foot-Loose Doll".
This episode (and at least one other) features an instrumental of the song "You Need Us," which was sung by the Honeybees on Don't Bug the Mosquitoes (1965).
The hired killer played by John Rayner is listed in the credits as Tierney, but at no time in the episode is the character ever named.