Revealing Mistake: When Barbara and Jenny are held prisoner by the Daleks, they have to hold their neck manacles (and the Dalek sucker pads) in place.
Continuity: In World's End, one of the windows on the Tardis was tilted in. In this episode, it has returned to being closed.
David: I'll say one thing, Doc: life's never dull with you around.
the Doctor: Thank you, but don't call me "Doc". I prefer "Doctor".
Susan: [distressed] Grandfather
The Doctor: Listen, Susan, please. I've double locked the doors, you can't get in, now move back child where I can see you.
[Susan steps back outside the TARDIS, the Doctor pauses inside about to say something he's clearly going to find difficult]
The Doctor: During all the years, I've been taking care of you, you in return have been taking care of me.
Susan: Oh Grandfather I belong with you.
The Doctor: Not any longer Susan. You're still my grandchild and always will be, but now you're a woman too. I want you to belong somewhere, to have roots of your own. With David you'll be able to find those roots, and live normally like any woman should do. Believe me my dear, your future lies with David and not with a silly old buffer like me.
[The TARDIS dematerialises]
The Doctor: One day, I shall come back. Yes, I shall come back. Until then, there must be no regrets, no tears, no anxieties. Just go forward in all your beliefs, and prove to me that I am not mistaken in mine. Goodbye, Susan - goodbye my dear.
The Doctor finally does keep his promise to Susan to return one day and visit her in the Eighth Doctor novel, Legacy Of The Daleks written by John Peel and published by BBC Books (ISBN 0 563 40574 0) in April 1998. The Master shows up and tries to make the most of the remaining Dalek technology, while the Daleks themselves may not be entirely gone from Earth. Characters from The Dalek Invasion of Earth, such as Craddock and David, who does not live to see the end of the story, return.
The scene of the Doctor saying goodbye to Susan is reused as a pre-credits sequence on The Five Doctors.
Final regular appearance of Carole Ann Ford as Susan Foreman. She was the first member of the original cast to leave the show. She appears next in The Five Doctors.
The character recounts an alternative personal history in a radio play, Whatever Happened to... Susan. Starring Jane Asher as Susan and James Grout as Ian, this was first broadcast on BBC Radio 4 on 9 July 1994.