In this, Tennant’s penultimate episode (if you count both parts of “The End of Time” together, that is), we begin to see the Doctor fighting against time itself. When he pilots the TARDIS to land on Mars, he only wants to enjoy himself (as he states when questioned, his name, rank, and purpose are “The Doctor, doctor, and fun”). However, he finds himself landing on the red planet at a very bad time: the year 2059, on the day that humanity’s first base on Mars is to be destroyed for unknown reasons.
Before he can bring himself to leave, he is captured by the team on the base: eight colony members led by Captain Adelaide Brooke. The Doctor is familiar with her, mostly because he knows that she is destined to die and set off a chain of events that will inspire her descendants to go into space and establish peaceful relations between humans and extraterrestrial species. This event, as the Doctor puts it, is “fixed in time.”
That’s when the fun begins. And by fun, we mean a water-born parasite slowly beginning to turn the entire crew into zombies which can spray infected water all over anyone, spreading the parasite to everyone involved. It’s a rather dark episode, and not just because of the zombified faces of the parasites’ victims. Amid the claustrophobia of the base, which is slowly starting to be flooded by the water, the Doctor begins to let his power go to his head; he thinks that he’ll be able to stop fate and rescue the crew, which looks more and more unlikely with each crew member who is infected (some very sad and chilling scenes here, which are beautifully written). Adelaide, finally convinced that the Doctor is right and that she must die, decides to destroy the base, but not before the Doctor rescues here and two colonists from the base, transporting them back to earth in the TARDIS.
Here’s where the real zinger comes in. After seeing off the two colonists, Adelaide admonishes the Doctor for saving her life, as she had come to believe the “fixed in time” theory more than he did. Rather than risk changing the future, Adelaide takes her own life as the Doctor looks on sadly, realizing that he is becoming too powerful. As he goes to re-enter the TARDIS, he realizes that the time is coming for him to die, though with the closing moments of the episode, he shows his intention to fight this. It’s a great bit of character development, as the Doctor finally tries to stop fate instead of just accepting it. And at times, this episode can be rather scary too, in a sort of 28 Weeks Later kind of way.
“It’s what’s in the dark…” >>