There are a lot of threads and references to unpick in "The Sound of Drums," as befits a story that not only returns one of the Doctor's most notorious enemies to full glowing health, but also adds new strands to his personal mythology. He's every bit as comically sadistic as he has ever been, but with a tortured undercurrent, having been driven to distraction by drumming that only he can hear.

It is also the beginning of the end of Martha's unrequited love for the Doctor, as she realizes the danger he has brought to her home (which is blown up) and family. Plus he is suddenly made to look a LOT older, thanks to the Master's laser screwdriver, and that can't help but change things a bit.

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 Toclafane were based on an idea Russell T Davies had developed before Doctor Who had been reborn, and nearly used as a stand-by monster for two previous stories. When the newly-resurrected Doctor Who temporarily lost the rights to use the Daleks, the story "Dalek" would have featured a small evil floating sphere with a childlike personality, which turned out to be a mutated form of humanity from the far future. Luckily the rights issue was resolved, but the idea remained (although they were called Roclafane at the time, which was changed to avoid confusion with the Racnoss). They also nearly appeared in "The Satan Pit," when budget constraints made the idea of computer animating the Beast seem unlikely.

Martha's joking question about the Master being his secret brother, and the Doctor's response about her having watched too much TV is a nod to a rumour that the First Master would have been revealed as the Doctor's long lost sibling during the classic Doctor Who's tenth season, but for the untimely death of Roger Delgado, who played him. The Doctor has stated that he has (or rather had) a brother, albeit one we've yet to see onscreen. He's been named as Irving Braxiatel in both Doctor Who novels and audio dramas, although his personal archive of rare artefacts and pieces of artwork, the Braxiatel Collection, is referenced in the Fourth Doctor story "City of Death."

As the Master triggers the rift above the Valiant and allows the Toclafane through, he plays the song "Voodoo Child" by Rogue Traders, which had been a firm favorite of Russell T Davies' while writing this episode. A dance track based on the main refrain from "Pump it Up" by Elvis Costello and the Attractions, the song had been a U.K. chart hit in 2005, and not only gave this episode its title, it added a note of unhinged levity to what is, for humanity, a desperate situation:

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

The Master is seen enjoying an episode of Teletubbies that echoes a previous scene from episode one of the Third Doctor story "The Sea Devils," in which his first incarnation is seen taking an active interest in the BBC children's animation The Clangers, whom he at first considers to be "a rather interesting extra-terrestrial lifeform" until he is informed they are "only puppets you know, for children" at which point his interest wanes.

There's a further nod to the Master's past when he begins his global address, "peoples of the Earth, please attend carefully." It's clearly a phrase he likes to use whenever he gets the chance, as his second incarnation made a similar speech in the Fourth Doctor's final adventure "Logopolis," which began "peoples of the universe, please attend carefully."

Another wink to fans of classic Doctor Who is the Master's offer of a jelly baby to President-elect Winters. Over the years, the jelly baby has become a totemic sweet for Doctor Who, just as Jammie Dodgers are the totemic biscuit. First introduced by the Second Doctor as a way to pass the time during "The Dominators," they have often appeared in the pockets of his subsequent incarnations. But it was the Fourth Doctor who showed a real affection for them, using them to diffuse tense situations and charm suspicious guards and soldiers alike. They were last seen being offered around by the Twelfth Doctor from a very nice cigarette case in "Mummy on the Orient Express."

https://www.youtube.com/watch?v=geMx6y8ctFk

The Master yells, "But tonight, Martha Jones, we've flown them in all the way from prison," as he gloats over his capture of Martha's family. The way he says it is an echo of the TV show This is Your Life, in which celebrities meet up with old friends and lost family members, as introduced in flamboyant style by the show's host, Eamonn Andrews.

When we see the young Master gazing into the rift, he's wearing a monochrome robe similar to those worn by the Time Lords in their first TV appearance, the Second Doctor regeneration epic "The War Games." The adults are seen wearing the classic Gallifreyan robes, including the distinctive collar headpiece, first seen in the Fourth Doctor story "The Deadly Assassin." The collars worn by the actors in this episode were actually the ones made in 1976 by the BBC's James Acheson, having been borrowed from the Doctor Who Exhibition in Blackpool.

The actor playing the young Master, William Hughes, once played an even younger David Tennant, having been given the role of the child Casanova in Russell T Davies' TV series about the famed lothario, from which David Tennant impressed Davies enough to be offered the role of the Doctor after Christopher Eccleston left.

During the sequence of Saxon campaign endorsements from celebrities, we see Sharon Osbourne and the former Conservative MP Anne Widdecombe. In the middle is the pop group McFly, who were at the peak of their popularity at the time with chirpy ditties like this:

https://www.youtube.com/watch?v=JiyF3K7hFqM

NEXT: 10 Things You May Not Know About ‘Last of the Time Lords’

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