Revealing Mistake: The clip of the TARDIS materialising in space is a reused clip from given the fungus appearing on top.
Revealing Mistake: One of the walls in the wide shot of the TARDIS console room is clearly a photographic blow-up.
With this episode the character of Jamie MacCrimmon has appeared in 20 Doctor Who stories for a total of 113 continuous episodes. This makes Jamie's tenure in the TARDIS the longest of any of the Doctor's travelling companions.
The Doctor: Goodbye, Jamie.
Jamie: But Doctor, surely we could…
The Doctor: Goodbye, Jamie.
Jamie: I won't forget you, you know.
The Doctor: I won't forget you. Now don't go blundering into too much trouble, will you?
Jamie: You're a fine one to talk!
The Doctor: Goodbye, Zoe.
Zoe: Goodbye, Doctor. Will we ever meet again?
The Doctor: Again? Now, Zoe, you and I both know time is relative, isn't it?
Time Lord: You have heard the charges against you: that you repeatedly have broken our most important law, of non-interence in the affairs of other planets. What have you to say? Do you admit these actions?
The Doctor: I not only admit them, I am proud of them! While you have been content merely to observe the evil in the galaxy, I have been fighting against it!
Time Lord: It is not we who are on trial, Doctor. It is you.
The Doctor [ sarcastically ]: No, no, of course, you're above criticism, aren't you?
The Doctor: You can't just change what I look like without consulting me!
This episode marks the first appearance of the Time Lords, after first being mentioned in Episode Six of this story. Up until this point the Doctor's origins were a complete mystery
This episode marks the final regular appearance of Patrick Troughton as the second Doctor, as well as Frazer Hines as Jamie MacCrimmon and Wendy Padbury as Zoe. However Troughton's second Doctor will return to the series on three more occasions: The Three Doctors, The Five Doctors and The Two Doctors. Jamie returns with the Doctor in the first and last of these adventures: phantoms of both companions appear in The Five Doctors.
Interestingly, Clyde Pollitt and Bernard Horsfall, who play two of the Time Lords, would later return as Time Lords: Pollitt as the Chancellor in Season 10's The Three Doctors and Horsfall as Chancellor Goth in Season 14's The Deadly Assassin. Presumably, they are playing the same characters in both appearances.
This was the final black and white episode. Episodes from next season would be in colour.
The first occasion on which the Doctor feels the force of the Time Lords as they try to capture him and put him on trial. See also The Trial of a Time Lord, Part Eight.
This story features the Doctor's second, and only forced, regeneration, as the Time Lords impose a change of appearance as well as exile to Earth. It is unclear how precisely they triggered the regeneration, or how they were able to determine the form of his new incarnation. The full horror of the punishment - effectively an execution - was not made clear until later in the series. See The Planet of the Spiders, Part Six and The Deadly Assassin, Part Four.
At his trial, the Doctor shows the Time Lords some of the evils he has encountered: the Quarks, the Yeti, the Ice Warriors, the Cybermen and the Daleks. A Kroton was supposed to appear as well and a payment was sent to their creator, Robert Holmes but in the end, it wasn't used.
Clips of the TARDIS in space (from The Web of Fear, Episode 1) and landing on the sea (from Fury from the Deep, Episode 1), and of a space station (from The Wheel in Space, Episode 1) were also shown.
The Doctor's trial and exile to Earth marks the beginning of a major format change that lasted for the next few seasons.
A fan theory supported by the later original novels from BBC Books claims that the Doctor's trial in this episode was only a show trial, and that his second incarnation was forced to carry out "community service" for the Time Lords for quite some time before his forced regeneration and exile to Earth. This is the "Season 6b" theory.