squid Kroll, causing it to turn into a gigantic monster. The final segment is a female humanoid – Princess Astra. Casting Main cast Tom Baker as the Fourth Doctor Mary Tamm as Romana John Leeson as Voice of K9 Guest Cast Valentine Dyall as the Black Guardian Tom Baker continued his role as The Fourth Doctor, and saw the introduction of Romana played by Mary Tamm. This season was the only one to feature Tamm as the first incarnation of Romana, as Tamm left the programme after only one season because she felt that the character had reverted to the traditional assistant role and could not be developed further. The second incarnation, played by Lalla Ward (who also appeared in this season as Princess Astra), began her run in the first serial of the next season (Destiny of the Daleks). Serials Douglas Adams took over as script editor from Anthony Read for The Armageddon Factor. Season 16 consists of one long story arc encompassing six separate, linked stories. Broadcast The Key to Time was broadcast from 2 September 1978 to 24 February 1979. Home media VHS releases DVD and Blu-ray releases In print References Bibliography 1978 British television seasons 1979 British television seasons Season 16 Season 16 16 Fictional cubes