31 October 1964: broadcast of "Planet of Giants", first episode of the story we also now call Planet of Giants, starting Season 2 of Classic Who. The Doctor, Ian, Susan and Barbara arrive in contemporary England, but miniaturised; they witness a murder and face peril from a cat.
31 October 2009: broadcast of Regeneration, the first episode of the K9 spinoff series. In a totalitarian London in 2050, K9 Mark 1 appears, regenerates, and teams up with teenagers Starkey and Jorjie. (This is the only episode I have seen but I enjoyed it.)