Here's a rarity from the ABC Saturday Superstar Movie.
The cast of Nanny & the Professor reunited for "The Phantom of the Circus", in which Professor Everett (Richard Long), Phoebe (Juliet Mills), and the kids not only take in a circus performance, but solve a mystery at the same time, with the help of Uncle Skylark, a Sherlock Holmes lookalike (Bernard Fox, Bewitched).
Presented for your perusal. I hadn't seen this previously, so I won't rate it.
Edit, 9/21/16: Had to post a fresh video. This one replays the first 8 minutes after the credits roll.