Cast as a Mask: Marlyn Mason in "Who Killed Helen French?" as Angela Somes who turns out to be Helen French herself, using makeup to hide the facial bruises she received from her abusive husband and a wig to hide her short hair as part of her double life - "Angela" is a lady of the night and Helen-as-Helen escapes when her husband thinks he's killed her (due to drunkenness). Note how in act 1 when her husband beats her we never see her face.
Dawson Casting: Usually averted - in "No Minor Vices" Cindy states she's 18; she's played by Maureen McCormick, who was 19 at the time of filming - but played straight in "One Last Trick," when a callgirl called Sheila (played by Deirdre Berthrong, around 24 when the episode was shot) says she's 17.
Ever wanted to see Bill Bixby as a ruthless assassin? "Target: Red" is for you.
What Could Have Been: The show's only two-parter "The Thrill Killers" was originally planned to air as a two-hour season premiere (which is why Part 2 has Acts V-VIII), but Fred Silverman insisted that it be split in two so that the second part could go up against the season premiere of fellow QM Production Barnaby Jones on CBS and hopefully beat it in the ratings. (It didn't work. Plus it turned out to be the final season for The Streets of San Francisco, whereas Barnaby Jones ran until 1980.)