The Doctor is surprised on a ridge, staring down at the lovely base, by a robot with a gun. It's grimy-white, dingy and spidery, kludged together. Not shiny. He goes "Gadget-Gadget" when he talks, and his name is Gadget. We're going to pretend he doesn't exist, to the degree we're able. Bit later Adelaide's pointing a gun at the Doctor: "State your name, rank, and intention."
"The Doctor. Doctor. Fun."
Say what you will, but Lady Christina de Souza at least gave him that back. As much as Jackson Lake reminded him to be brave. The crew runs around yelling about how there's a mysterious man on Mars and how exciting this is for them, and Adelaide tells them to shut it, and the Doctor babbles at her about not pointing the gun at him, and she goes -- this bit is funny -- she goes, "Oh, you'd like that!" And you know, like, "Can you find me someone who wouldn't?" Brooks asks him why she should trust him, and he gives her his word, and points out that forty million miles away from home, that's all she's going to get.
They lock eyes and he does that thing he does, and she drops the gun but keeps the robot trained on him. So now he has a whole conversation about the robot with the robot driver, who is a sort of unbalanced-seeming emo kid that looks like he smells of energy drink and desperate masturbation, and then we transition via a comms link interchange (with more of that "She's the boss and hard-ass but wink-wink" stuff where nobody really listens to her but everybody fiercely loves her) to the lovely hydroponics garden area, where two more crew are chatting at length about this and that. They talk about how they love plants and how this is a New Eden and whatever, and as she's advancing the theory that the new man on Mars is from the Philippines, or maybe Spain, he's dying.
He bites into a carrot, he falls to his knees, and shivers, first quietly and then violently, and somewhere in there he's dying. He doesn't answer her with speech. There is the sound of water. She tries to get his attention, and finally he turns. His face is terrifying: Broken lips, water everywhere and coming from everywhere, plastering his hair to his face. Black teeth, white eyes: A negative, a reversal. It's uncanny, and as everyone said when they saw the episode, more frightening than it has the right to be.
The Doctor has quickly become bored with the crew's ongoing attempts to guess at his origin ("Was it the Branson inheritance lot? They've talked about a Mars shot for years") and finally kicks them forward, into the story.