Doctor Who: Revenge of the Cybermen / Silver Nemesis (DVD)

This BBC box set of Doctor Who: K9 Tales unites two classic Dr Who stories: The Invisible Enemy and the first Doctor Who spin-off K9 and Company. It's also packed with a host of fantastic extras. Starring Tom Baker, The Invisible Enemy is a four-part story featuring the screen debut of K9, the robot canine. When The Doctor answers a distress call from a shuttle crew who have been infected with an intelligent virus, he too becomes contaminated.

K9 and Company sees the Doctor's two companions, Sarah Jane Smith (Elisabeth Sladen) and K9 appearing together. Also known as A Girl's Best Friend, this was the first bona fide TV spin-off from Doctor Who. In this one-off special, Sarah Jane pays a Christmas visit to her Aunt Lavania in the village of Moreton Harwood. But something is horribly wrong. Lavania is missing, leaving Sarah Jane in charge of her aunt's ward Brendan. When Brendan is kidnapped by an evil cult of witches, Sarah Jane and K9 find themselves in the middle of a mystery.