The Sound of Drums

The Doctor, Martha, and Jack manage to escape from Futurekind in the year 100 trillion through Jack's repaired Vortex Manipulator, finding themselves in London. They quickly learn that the Master has taken on the persona of "Mr. Harold Saxon", the current Prime Minister, using his Archangel phone network to subliminally influence the population into voting for him while masking his presence from the Doctor. The three narrowly avoid a bomb placed in Martha's flat, and the arrest of Martha's family, before the Master contacts them to gloat about his seeming victory.
The Doctor learns that the Master was resurrected by the Time Lords to fight in the Time War to be the perfect warrior, but instead the Master fled to the end of the universe and made himself human when defeat seemed inevitable. The Master reveals that the three are now England's most wanted criminals and has stripped them of any help, including sending Jack's Torchwood team on a wild goose chase to the Himalayas. Hiding in an abandoned building, the Doctor uses parts of Martha's laptop and the TARDIS keys to create a perception filter so they can move about unnoticed. He explains some of the Master's past: that as a child, the Master looked into the Time Vortex, and was likely driven mad as a result. They come to discover that the Master, as Saxon, is planning to reveal Earth's first contact the next day with an alien race known as the "Toclafane", (in truth, the name 'Toclafane' refers to the Gallifreyan equivalent of the "bogeyman",) and the Doctor insists they must be present.
As the appointed time of first contact nears, United States President-Elect Winters arrives in England and places the operation in the hands of UNIT, transferring the meeting aboard the flying aircraft carrier, the Valiant; the Master accepts this change, as it suits his purposes, and along with his wife Lucy and the rest of Martha's family, board the vessel. The Doctor, Martha, and Jack teleport aboard with Jack's vortex manipulator, discovering the Doctor's TARDIS has been "cannibalised" by the Master to create a Paradox Machine which is building up power to be activated at the appointed time of first contact.
As the three make their way to the bridge, the Doctor tells them to try to get their perception filter around the Master to reveal who he really is to humanity and stop his plan. As they enter the bridge unnoticed, the first four Toclafane, floating metal spheres, appear on the bridge and demand to see the Master; the Master delightedly reveals himself and orders the Toclafane to kill Winters. The Master then reveals that he is well aware of the Doctor's presence in the room by using his laser screwdriver upon the group, temporarily killing Jack while aging the Doctor by 100 years through the use of LazLabs genetic manipulation technology using biological data from the Doctor's severed hand that the Master had stolen. Jack gives Martha his vortex manipulator and tells Martha to get off the Valiant, as there is no way they can defeat the Master.
The Master brings Martha's family into the bridge as the Paradox Machine nears activation, and taunts the aged Doctor about the nature of the Toclafane and his victory. The Paradox Machine activates as the Master tells the people of Earth that it's the "end of the world" and plays the song "Voodoo Child". A massive rift opens above the Valiant, and six billion Toclafane descend from it. The Master orders the Toclafane to "remove one tenth" of the Earth's population. As Martha tends to the aged Doctor, he whispers into Martha's ear. Martha, unable to save the Doctor, Jack, or her family, promises she will return, and uses Jack's vortex manipulator to teleport off the Valiant to find safety on Earth; she then flees into the distance as the Toclafane wreak havoc on humanity. The Master himself gloats about the fall of the human race and forces the Doctor to look upon his "new dominion as Master of All."