Continuity; The crown on K-9 relocated from around his ears to the back of his head while the Doctor is modifying Andred's helmet.
The Doctor: That's why I've plugged K-9 into the Matrix instead of me. He's got no brains, you see. Sorry about that, K-9.
Andred: Can you trust a machine?
The Doctor: This one, I can. He's my second-best friend.
The Doctor: I don't know what they teach you at the Academy these days, but if you can't pull off a simple palace revolution, what can you pull off, hmm?
Andred: What treachery are you attempting now?
The Doctor: A rather more effective treachery than yours, I hope.
Andred: Die, traitor!
The Doctor: Not now, can't you see I'm busy?
The Doctor: Have you ever thought of taking it up seriously?
Leela: Taking what up seriously.
The Doctor: Well, killing people. With a little practice you'd become quite proficient.
Andred: But you have access to the greatest source of knowledge in the universe.
The Doctor: Well, I do talk to myself sometimes...
Andred: I meant the Matrix.
The sound effects when the Doctor is opening the shield for the Vardans is identical that used in The Deadly Assassin when the Master accesses the Eye of Harmony.
Some omnibus versions of this story distributed for PBS in the U.S.A. make a very sloppy edit due to credits removal. The surprise revelation of who has invaded Gallifrey is completely ruined when the Sontarans suddenly appear after a brief blackout.
Relief of Mafeking: The Doctor references this pivotal battle from the Boer War.