K-9 and Company, on BBC One (UK)
This was supposed to be a spin-off of Doctor Who, but it never made it past the pilot episode ("A Girl's Best Friend"). I originally put this entry in the TV movie section, since I'm pretty sure I had seen it presented as a TV movie, at some point. At least, that's how I remembered it, years later, when I started doing TV reviews. (I don't remember exactly when I saw it. It originally aired in the UK in 1981, but it must have been at least the late 80s before I saw it, and it may have been the 90s.) Eventually I decided to move this to the specials section, because apparently it had been aired as such in the UK. (And because it's actually shorter than I remember it being. Probably I would have seen it on public television, so I'm guessing there was at least one pledge drive break during the broadcast.)
Anyway, it's about one of the Doctor's companions, Sarah Jane Smith, who went back to her old life on Earth after her travels in space and time with the Doctor. And she found a package waiting, which he'd left for her. It was K-9 Mark III. (On the series Doctor Who, the Doctor had at one point gotten a computer dog named K-9 from some scientist in the course of his adventures. The first K-9 later stayed on Gallifrey with Leela, and the Doctor got a second one, K-9 Mark II.) Sarah Jane and K-9 had some odd adventure which involved Druids and Stonehenge, or something. It wasn't all that good, but I still would've liked the series to have continued a bit. One of these days I shall have to rewatch the thing and write up a proper review.
Meanwhile, Sarah Jane finally got a new spin-off series in 2007, called The Sarah Jane Adventures. It ran for five seasons, but I've only been able to see the first.