K-9 is set in near-future London, with 14-year old characters Starkey and Jorjie, alongside a Professor Gryffen, who is experimenting with a Space-Time Manipulator, and 15-year-old Darius who runs errands for Gryffen. K-9 Mark I follows the villainous reptilian warrior Jixen who come through a space-time portal created by the professor's experiments and saves the Londoners. While protecting them, K-9 is forced to self-destruct, but is able to give Starkey instructions to rebuild and regenerate himself into a more advanced form. K-9 and the humans then form the front line defence against alien menaces from outer space and other times. The Brisbane Times reports that the series is set in London in the year 2050 and Professor Gryffen is employed by a clandestine government agency, "The Department". The design of K-9 is noticeably different from that seen in Doctor Who because although Bob Baker owns the character rights to K-9, the original character design is owned by the BBC.