The Doctor, Vicki, and new companion Steven Taylor arrive in Saxon Northumbria on the eve of the Viking and Norman invasions. It is 1066, a pivotal moment in British history. The hand of a mysterious Monk is at work in the nearby monastery, intending that history takes a different course.
The Time Meddler was the ninth and final story of season 2. This story was the first pseudo-historical: an historical story with science-fiction elements other than the presence of the regular characters and the TARDIS.
The Monk was the first Time Lord other than the Doctor and Susan to appear in the series, although the term Time Lord would not be invented for another four years. The Monk also became the series’ first recurring individual villain.
This story contains the first reference to what would become the Time Lords’ non-interference policy. Although the Doctor never mentions it directly, he clearly shuns those who meddle with time. As in The Space Museum, time is shown to be theoretically malleable, in contrast to the view of time presented in The Reign of Terror. The concept of time would later be expounded upon to incorporate both elements in numerous later stories, including Attack of the Cybermen. [tardis.wikia.com]
A surprise for the Monk on the Doctor Who YouTube Channel.