There's a bit of Hollywood history in this episode.
Prolific writer Stanley Roberts wrote this story, who wrote the screen version of THE CAINE MUTINY for Humphrey Bogart, also the screen version of DEATH OF A SALESMAN for Fredric March. Roberts was very selective and producer Quinn Martin was lucky to have him on board. This was his only story for the show.
I agree with the last reviewer; the death of billionaire Howard Hughes at the time may have inspired the episode in the first place. Pretty Susan Day (PARTRIDGE FAMILY), proves herself a fine dramatic actress, playing a young woman who hires Barnaby to look into the supposed suicide of her mom, connected to a Hughes type businessman who recently died.
Of course, there's some diabolical folks in the way, who want to get their hands on the old man's millions, also responsible for her mom's death. What a tangled web. Well written material that will keep your attention throughout.
Top cast, co-starring Pernell Roberts as Daniel, screen star Nancy Olson as Thelma and series regular Roger Perry as Glenn. Olson had retired from films in the 50s, but return to Hollywood in the 60s and 70s in various character roles, and she's quite good here.
The mansion featured is in the Los Feliz section of Hollywood, where MANNIX filmed so many episodes. The estate, on Waverly Drive, is the former home of a car dealership and radio tycoon, and is now either the home of singer Katy Perry or next to her mansion. Location, location, location!
Watch this for some top stars. SEASON 5 EPISODE 13 remastered CBS/Paramount dvd box set.