The Dalek Invasion of Earth has a significant place in the ongoing development of the series. It’s the first returning “monster”, the first companion departure, and the first story to feature more than a few moments of outdoor filming. The latter gives it a less claustrophobic feel than many prior serials and gives a potentially large canvas on which to draw for gaming, aided by the fact that it’s also the first story to be set on Earth in the future. It’s almost universally cited as one of the better stories of the Hartnell era, sometimes even the best overall. And, in this instance, the setting also happens to be one that lends itself well to gaming.
Where & When
The exact date is never given in the story, but we do see an old 2164 calendar, so it’s no earlier than that. While there is some wiggle room depending on exactly how old the calendar is, based on a line in a later story, fan consensus generally takes the year as being 2167. The story is initially set in London and later moves to Bedfordshire.