The Waters of Mars

The Doctor arrives on Mars, apparently just to relax and enjoy the landscape. At the same time we see an officer (who turns out to be Captain Adelaide Brooke) talking to her family on Earth via a comlink, from a station which transpires to be on Mars. Happening upon the base, the Doctor is arrested by a remote-controlled robot and brought before the Captain. Brooke is initially suspicious of the Doctor, but after a sharp conversation, decides to trust him. The Doctor learns that the date is 21st November 2059, and that this is in fact Bowie Base One, the very first human outpost on Mars. He recalls that, according to history, on this date the base was destroyed in a mysterious explosion in which Brooke and her crew were all killed. Unwilling to break the laws of time and interfere with fixed points in history, he decides to leave, but at the very same time a crisis is developing: one by one, the crew of the base are being infected by a mysterious life form which takes over their bodies, causing them to gush copious amounts of water. Adelaide confiscates the Doctor's spacesuit, reasoning that he could be responsible for the infection in some way, and orders him to come with her and her subordinate, Tarak Ital, to investigate two affected crewmembers, Andy Stone and Maggie Cain, who are not responding to radio calls from the control centre.The infection rate soon begins to increase rapidly, with Andy spreading the condition to Tarak. The two men are contained in the bio-sphere (a "greenhouse" section of the base) while Maggie is secured in the medical wing. Meanwhile, the Doctor is more desperate than ever to leave history to follow its course. The crew plan to evacuate, and the Doctor breaks the news to Adelaide that she must die today, on Mars, if events are to unfold as they should. He cannot shape her destiny, but tells her that her death will inspire her descendants to travel beyond Mars and establish peaceful relations with numerous extraterrestrial species. After he explains this to Adelaide, she lets him go — but, overcome by defiance against time itself, and reasoning that since he is the last of the Time Lords he has the right to control time, he returns to the base, declaring, "The laws of time are mine, and they will obey me!"Using Gadget, the remote-controlled robot, the Doctor brings the TARDIS into the base, rescuing the final three survivors from the conflagration of the base's nuclear destruction. During this time Adelaide realises that he is doing wrong, and should be doing so, as he knows about the pre-determined events.After landing on Earth, Mia and Yuri, shocked at the previous events and the Doctor himself, leave. In a conversation with Adelaide, the Doctor reflects on his changed attitude, which includes calling Mia and Yuri 'little people'. He claims to have realised that the rules of time were valid only when the Time Lords still existed, and that now he is the only Time Lord, he makes the rules, dubbing himself the 'Time Lord Victorious'. Brooke chides him for his newfound arrogance and dominance and to preserve the integrity of the time stream, returns to her house and commits suicide. Suddenly, and horribly stricken by both her and his own actions, realising he has broken the rules and that there must be a price, the Doctor sees Ood Sigma appear in the street, and asks him whether he has finally gone too far — whether this is his death.Unresponsive, the Ood vanishes, and the Doctor staggers back into the TARDIS, to the ominous sound of the Cloister Bell, which only chimes when disaster looms. He suddenly declares "No", and begins to work the TARDIS controls.