Wow! This was one of the best Dr. Who's I've seen in a long, long time. In past episodes, the doctor always tried to stick with what history said. If a civilization died out, then he made no attempt to save anyone to make sure that history remained intact, (Of course the Pompeii episode with Donna was a bit different, as she bothered him senseless until he saves three or four people, I think).
With this one he suddenly decides that because he is a Time Lord that means he can change history if he likes and does, to some extent. After he saves the last three people from the destruction of the base on Mars, he takes them home to earth.
For just a bit it looks as if doctor has become a bit unbalanced. He becomes, well more than a tad arrogant and tells Adelaide that he can change history now whenever he chooses. He is after all not just a survivor of the Time Lord wars with the Daaleks, he the winner. He's quite proud of the fact that he changed history and like I said arrogant with it, even after Adelaide tells him that no one should have that much power.
He jokes around as only the doctor can and takes his leave of Adelaide, but Adelaide who was supposed to die on Mars, ends her life in her home on earth.
The doctor realizes that he did change history, kind of. He only changed the location of her death and the rest of history proceeds as it should have.
Although I thoroughly enjoyed this episode, I'll admit that it scared the poop out of me. I hate zombies and those things were as close to zombies as they could be. Yeah they were ugly, but their biggest problem was moisture. The water was literally pouring out of their entire bodies; mouths, ears, pores. While the idea of another imminent invasion of the earth seemed apparent, that wasn't what I found interesting about this episode. The change in the doctor was what grabbed my attention. First, he was like his old self, wanting only to keep history intact whatever the cost. Second, as he's walking away from the people on the base, you see that he's fighting himself and what he knows to be the right thing to do and allows himself to be swayed. Third, after he saves the people and gets them to earth, his attitude changes. It's not about the fact that he saved people that makes him happy, he even refers to Adelaide's subordinates as lesser people, it's that he has the power to do anything he wants. He allows the power that he used to go to his head and change him. Arrogance rears it's ugly head and it doesn't make him look very attractive. Fourth, when he realizes that he wasn't really able to change history he becomes lost, afraid and runs to hide like a trapped animal in his ship.
I don't if this episode was meant to convey anything or if it was just entertainment pure and simple, but I felt like it was saying that as with most humans power can and does corrupt absolutely, unless there's something there to put a stop to it.
Thank you so much for posting this wonderful episode. Now I'm looking forward to the Christmas episode. I can hardly wait!!