Ep 16. The Waters of Mars

The Doctor lands in a human colony on Mars in the year 2059. The colony, Bowie Base One, is run by Captain Adelaide Brooke, a legendary commander in Earth's history, and her team of astronauts. As the Doctor tries to blend in with the crew, he senses something is wrong. He discovers that the base is under attack by a mysterious water-based life form that can infect and possess people. The infected crew members turn into zombie-like creatures, which terrifies the remaining crew.

The Doctor discovers that the water-based life form has been dormant on Mars for centuries, but it was brought back to life by scientists searching for ways to colonize the planet. The life form possesses one of the crew members, and the Doctor urges Adelaide to quarantine the base and evacuate all the human inhabitants immediately. But Adelaide refuses to leave, insisting that it is her duty to die on Mars to keep human history from being altered.

As the situation becomes increasingly dire, the Doctor realizes he cannot save everyone and decides to take matters into his own hands. He uses his knowledge of future events to become a hero to the crew, but his actions lead to tragic consequences. The Doctor must face the fact that he cannot always save everyone and that every action has a consequence.

As the episode comes to a close, the Doctor returns to his TARDIS, where he is confronted by a mysterious woman named Ood Sigma. She tells the Doctor that his future will be full of darkness and that his "song is coming to an end." The Doctor looks worried and troubled, knowing that there are more challenges and battles to come.

Overall, "The Waters of Mars" is a gripping and tragic episode that explores the themes of sacrifice, duty, and the consequences of playing God. The Doctor is forced to make difficult choices, and the episode shows the limitations of his power and the consequences of his actions. It is a must-watch for any Doctor Who fan.