While doing research for the EP of which this track is a part, (read: watching Doctor Who episodes...well, and reading up on the history of the series), I ran across the mention Doctor's nemesis, the Master. I wasn't aware that the Doctor had a nemesis, although it's obvious he has enemies too numerous to count.
It was after watching the last three episodes of Series 3 (the David Tennant Series 3), Utopia, The Drums of War, and The Last of the Time Lords that I realized this "rivalry" between the last two Time Lords would make for a very interesting musical exploration.
If you remember in The Drums of War, there is a rhythmic figure which plays a central role in the trilogy. A homeless man taps it out on his tin cup; the Master taps it out on the desk after he gasses the cabinet members.
When the Doctor and Master talk on the phone, the Master describes the drumming that is constantly in his head (and that has driven him crazy). And, the Master uses this rhythm in the Archangel Network as a means to control Earth's population. I decided to use this figure throughout.
Further, in The End of Time, Rassilon, the Lord President of Gallifrey reveals that the rhythm is a signal that was planted in The Master's head as a beacon, and also that the rhythm is the beat of a Time Lord's hearts.
And now, here's the fun part of this one. I was a trombonist in our local symphony orchestra at the time I was writing this track. For our Winter Concert one of the pieces we played was Mars, The Bringer of War from Gustav Holst's The Planets.
As we rehearsed Mars, at the same time I was working on the breakdown/middle section of Doctor and Master, it dawned on me that the predominant rhythmic figure in Mars is in fact exactly the same rhythmic figure referred to in those Doctor Who episodes mentioned above.
The thought also occurred that every time the Master appears, he brings violence and war. There's not a much more fitting way to represent the Master than by using a bit of Mars, The Bringer of War.