"Last of the Time Lords" achieves an almost impossible task: It brings to a close a season of Doctor Who that contains two inarguable dramatic peaks—"Blink" and "Human Nature" / "The Family of Blood"—without feeling in any sense like an anticlimax. If anything, it grabs hold of the wrung-out cloth of fan emotions and still manages to squeeze out a fresh bucket of liquid feelings.

It's also the episode during which one of the Doctor's companions changes the most. During her year on Earth, Martha Jones stops being the wide-eyed and lovesick trainee doctor to become something close to a secret agent. She's still the Doctor's human proxy, as she was during the invasion from the Family of Blood, but this time her job is far greater, and she returns with a greatly increased sense of her own capabilities. Small wonder she elects to let the Doctor go on his way at the end of the story.

Here are a few things that you should keep an eye out for, the next time you watch.

(The episode is available on iTunes and Amazon.)

The version of this episode that was shown on British TV is five minutes longer than the international version (the one you can see using the links above). Among the scenes cut from the longer version are an introductory fake galactic traffic report telling travelers to avoid "Sol 3," some of Martha's conversations with various members of the resistance, and a section in which the victorious Master sings and dances to the song "I Can't Decide" by the Scissor Sisters while harassing a silent Doctor in his wheelchair. The song's chorus has the apt lyric: "I can't decide whether you should live or die / Oh, you'll probably go to heaven, please don't hang your head and cry / No wonder why my heart feels dead inside / It's cold and hard and petrified."

The Master makes reference to two of the Doctor's former foes from the classic series, the Sea Devils and the Axons, both of whom he battled during his third incaration. The Sea Devils were amphibious humanoid Earth reptiles, water-dwelling cousins to the Silurians. Axons, by contrast, were the biological extensions of the scavenger entity Axos, a modular telepathic monster who grew to become the size of a spaceship in "The Claws of Axos." They could appear as golden headed humanoids or walking tentacle monsters:

https://www.youtube.com/watch?v=KGFOU8WvLxs

Zoe Thorne, who provided the childishly gleeful voice of the Toclafane, is also the voice of the Gelth from "The Unquiet Dead."

Professor Docherty makes this exclamation: "Oh God, I miss Countdown. Never been the same since Des took over. Both Deses. What's the plural for Des? Desi? Deseen?" which may need a little unpacking. Countdown is a hugely popular British quiz show about anagrams and math problems. It's one of the longest running TV game shows in the world. There are two basic rounds (and a nine-letter anagram to solve). In the letters round, contestents have 30 seconds to make the longest word possible from an almost random collection of nine letters. In the numbers round, they're given five small numbers and one large one, and they have 30 seconds to work out how close they can get to the large number by adding, subtracting, multiplying and dividing the smaller ones.

https://www.youtube.com/watch?v=E3vmoac0R2Y

Having been hosted since 1983 by the avuncular Richard Whiteley, his death in 2005 prompted a flurry of guest presenters, including the former sports broadcaster Des Lynam, and the singer and comedian Des O'Connor. The plural of Des, as with any proper noun that ends with an S, is Deses.

Martha's brother Leo Jones was more fully written into the script originally, but Reggie Yates was unable to commit to filming (he's a very popular broadcaster in the U.K.), so the line about him working as a slave under a different name was inserted to explain his absence.

In the early drafts of the script, Martha's last tube of decoy chemicals was to have been located in Downing Street, and Tom Milligan was the person who turned her over to the Master.

The Doctor is restored to his old self and levitates above the Master in an echo of a similar scene from the Third Doctor adventure "The Mind of Evil," in which the Master is exposed to his greatest fear, the sight of the Doctor looming over him and laughing contemptuously.

https://www.youtube.com/watch?v=EjJBy9mJeCA

There's an echoed line that shows how mentally close the Master and the Doctor are. As he lies in the Doctor's arms, refusing to regenerate, the Master says, "How 'bout that, I win," which is a reorganization of the Doctor's similar boast "I win, how 'bout that?" from "Dalek."

The idea that the Master's ring would be plucked from the ashes of his funeral pyre came along quite late in the production. So the hand used to pick it up was not played by a significant actress, to offer a clue for future episodes. It was in fact Doctor Who production manager Tracie Simpson. Russell T Davies, during the audio commentary for this episode, joked that it was "the hand of the Rani," referencing another notable rogue Time Lord from classic Doctor Who.

The final scene with Captain Jack was originally written to include sections of his opening monologue from Torchwood: "The 21st century is when it all changes and you've got to be ready," with a playful response from the Doctor. This was taken out because it was felt to be too much of a wink to viewers, potentially undermining the great revelation that was to follow:

https://www.youtube.com/watch?v=MogTR2RpcSU

NEXT: 10 Things You May Not Know About ‘Voyage of the Damned’

Now read the rest of the 10 Things You May Not Know About Doctor Who archive.