Sir Derek Jacobi (Professor Yana/The Master) previously played Martin Bannister in the Big Finish Doctor Who Unbound audio drama "Deadline" and a robot copy of the Master in the webcast Scream of the Shalka. Both productions were released in 2003 to mark Doctor Who's 40th anniversary. David Tennant (The Doctor) had a small, uncredited role as a caretaker in the latter.

John Barrowman's name appears to the opening credits for the first time in this episode.

After the Doctor, Sarah Jane Smith and K-9, the Master is the fourth character to appear in both this series and Doctor Who (1963).

This episode features archive footage from "The Parting of the Ways", "The Christmas Invasion", "Gridlock" and "Human Nature".

This episode marks the first appearance of the Master, the Doctor's greatest enemy, in Doctor Who since the 1996 TV Movie, in which he was played by both Gordon Tipple and Eric Roberts.

This is the third Doctor Who story in which David Tennant appeared to feature the Master. In 2003, Tennant played Colonel Brimmicombe-Wood in the Big Finish Doctor Who Unbound audio drama "Sympathy for the Devil" opposite Mark Gatiss as the Master. This production featured David Warner as the Doctor. Later that same year, he had a small role as a caretaker in the webcast Scream of the Shalka opposite Sir Derek Jacobi as the Master. This production featured Richard E. Grant as the Doctor.

The two parts of the regeneration scene, the first featuring Sir Derek Jacobi and the second featuring John Simm as the Master, were filmed a week apart.

Filming locations: Cardiff Bay (at the Wales Millennium Centre), a paper mill in Wales

(The Doctor gets the mechanism to work)
Professor Yana: How did you do that?
The Doctor: Oh, we’ve been chatting away, I forgot to tell you. I’m brilliant!

Martha: The Doctor sort of travels through time and space and picks people up. God, I make us sound like stray dogs. Maybe we are.
Professor Yana: He… travels in time?
Martha: Don’t ask me to explain it. That’s a TARDIS, that box thing. The sports car of time travel, he says.

"Professor Yana": Did you never think, all those years standing beside me, to ask about that watch? Never? Did you never once think - not ever - that you could set me free?!
Chantho: Chan-I'm sorry-tho! Chan-I'm so sorry...
"Professor Yana": You, with your chan and your tho driving me insane!
Chantho: Chan-Professor, please!
"Professor Yana": That is not my name! "The Professor" was an invention. So perfect a disguise that I forgot who I am.
Chantho: Chan-Then... who are you-tho?
"Professor Yana": (whispered) I am...the Master!
(The Master kills her)

(Having been mortally wounded by Chantho, Professor Yana/The Master is dying)
Professor Yana/The Master: Killed by an insect. A girl. How inappropiate! Still, if the Doctor can be young, and strong, then so can I. The Master... reborn!
(The Master regenerates into new, much younger body)

(The newly regenerated Master has seized control of the TARDIS)
The Master: Doctor!...Oh, new voice. (speaking in different tones of voice) Hello, hello, hello! Anyway, why don't we stop and have a nice little chat while I tell you all my plans and you can work out a way to stop me, I don't think!
Martha: Hold on, I know that voice!
The Doctor: I'm asking you really properly, just stop! Just think!
The Master: Use my name.
The Doctor: Master. I'm sorry.
The Master: Tough!