Marks the first appearance of the Time Lords' homeworld in the series, although it would be another five years before the planet was named.
By this episode, the series had not completely developed the concept of the Time Lords' regeneration ability and the departure of the Second Doctor is treated as simply a "change of appearance." However, with the later establishment of the plot device and the fact that a Time Lord can only do it 12 times before dying permanently, the ending of this episode takes on a tone of the Doctor being executed since he is forced to use a regeneration, thus shortening his lifespan.
The uniforms worn by the Time Lords are the same as the one worn by the 8-year-old Master in the 2007 story, Last of the Time Lords (2007).
In this initial appearance, the Time Lord culture (costumes, locations, technology, etc.) is very minimalist compared to the very detailed development to follow.
This episode is the first case of blank slating in the series: beginning with the next episode, the entire main cast is different with none of the regulars in this episode appearing. The only exception is Nicholas Courtney, who wasn't a regular during this story but had previously appeared and was yet to become a regular on the series.