I'm talking about "K-9 and Company," the original Doctor Who spin-off that never made it past the pilot stage. K-9 and Company made its debut on December 28, 1981, and featured Sarah Jane Smith (Elisabeth Sladen), K-9 (John Leeson), and a variety of new characters such as Brendan Richards (Ian Sears) and Aunt Lavinia (Mary Wimbush).
Here is the plot: Sarah Jane Smith moves to the country estate of her Aunt Lavinia at Christmastime in order to write a book. She is disappointed and confused that her aunt is missing and begins investigating her absence. (She was whisked away early for a unexpected lecturing tour in the States.) She is quickly joined by her aunt's ward, Brendan Richards, and then discovers a Christmas package from the Doctor: a mechanical dog named K-9!
It turns out that there is an active coven of Pagan in the area and they have targeted their aggression on Aunt Lavinia (because of some blunt anti-Pagan letters that she had written for the local newspaper) and Brendan (presumably because he's young and pure and his blood sacrifice is needed to help the crops to prosper). Brendan is eventually kidnapped by the Pagans and nearly killed on Midnight of the Winter Solstice. Fortunately, K-9's lasers and Sarah Jane's fighting skills save Brendan from death and defeat the coven!
Keep in mind that there is very little mystery to the identities of the coven. Pretty much everyone in town belongs to the coven. You know this because they were all revealed as members of the coven during the opening scene. The only mystery was the identity of the coven leaders.
I've always wondered what K-9 and Company would have been like if it had moved beyond the pilot stage? The mentioned that there were similar covens scatted throughout England. Would the show have focused on those covens? Would they have explored other threats? We'll never know, unfortunately!
Interesting notes. Ian Sears (who played Brendan) appeared in an early episode of "Morse" and Mary Wimbush (who played Aunt Lavinia) appeared in an episode of "Midsomer Murders."