Can I just start by saying that I loved this episode?
Okay, now to business. So David Tennant is the new Doctor, and apparently he doesn't control the TARDIS very well. But they arrive back in London, and meet back with Mickey and Rose's mom. We are informed that it is Christmas Eve, and the Doctor is sick, and must lay down. So they go back to the apartment, and Rose has a good 20 minute cry about how the Doctor is gone, and how everyone is going to die. Meanwhile, these plastic-faced Santa Clauses send a Christmas Tree of Doom to them, which the Doctor blows up, and, just before he collapses in bed again, informs them that something else terrible is going to come. Sure enough, the British government discover a new alien species with their new probe. With the Doctor out of commission, it is up to Harriet Jones (who we met in Season 1), the new Prime Minister, to deal with the threat. Using blood control, the Sycorax put 1/3 of the world's population on the edge of something, threatening to push them over if earth does not surrender. Rose continues to cry about how everyone is going to die, and they all go hide in the TARDIS. The PM and several of her people get transported onto the Sycorax ship, and the TARDIS takes Rose, Mickey, and the Doctor there as well, without them knowing it. Rose, trying to stand up for her planet, makes the Sycorax leader laugh. Then, suddenly, everyone can understand what the Sycorax is saying, because the Doctor is back!
Now here comes the good part: the Doctor comes out, and engages in a wonderful conversation with the leader of the Sycorax, which included existential ponderings, and references to the Lion King, as well as saving 1/3 of the world's population. Then he challenges the Sycorax to a duel, which he consequently wins, after growing back the hand that the Sycorax had cut off. The Sycorax does not honor the honor code, so the Doctor makes him fall off the ship. The Doctor sends the ship on its way, but Harriet allows "Torchwood" to blow it up. The Doctor, obviously, is furious, but I can also understand why she did it. It's sort of a moral dilemma, really: protect your planet, or save the lives of an alien species you know nothing about (save that they tried to take over your planet). But whatevs. The Doctor takes down her government with six words. Six.
"Don't you think she looks tired?" I love him so much. He gets a legit outfit from the TARDIS closet we never knew existed, and he and Rose ride off into the sunset...