What a bummer!
So the Doctor ends up at the first human Mars base, a few decades hence. He quickly realizes that the Benetton Ad running the place is doomed to die, and fights himself majorly to get out of the way. Seems the head of the project, in dying, will inspire the future of human galactic exploration through her descendents. Trouble is, he becomes quite taken with her -- as you will too -- and can't quite seem to let it go.
Creatures from long ago, imprisoned in Mars's glaciers by the wise Ice Warriors, attack the station's workers one by one, infecting them through the water. What this does is make you spazz out, get Creepy-Eye and Gross-Mouth disease, and then drool uncontrollably from your face and arms. It does not sound that terrifying but it is huge amounts of terrifying.
While the woman Adelaide watches her life's work and closest friends quickly done in, knowing she'll be dying presently, the Doctor continues to wig out about how he -- the similarity in title to "The Fires Of Pompeii" is no accident -- must protect this fixed moment, since that's his entire job as a Time Lord.
But then he goes Donna on himself and realizes that, as the Last of the Time Lords, he doesn't actually have to worry about it. He saves what's left of the crew, blows the beasties all to hell, and drops the survivors on Earth. That's when it gets interesting: Even the Dalek knew that Adelaide's life and death were off-limits, and left her alive as a child -- so what's that say about the Doctor's newfound carelessness?
One of the survivors is driven half-crazy by the TARDIS and runs off into the snow. Adelaide calls bullshit on the manic Doctor, explaining that nobody should have enough power to completely reroute timelines. In a last act of defiance -- and in the hopes of getting the Doctor's shit together for him -- Adelaide blows her brains out. While the Doctor reconsiders what he's becoming, the Cloister Bell starts ringing and Ood Sigma appears to him as a reminder that his song is ending after all.
You wanted her to love you.
That's what it comes down to, isn't it? You wanted to think there was a point. A point at which, a point at which the fear and the power would be overcome by the love. You wanted to go back to the place where everything was safe. Where somebody would stop you. But we're well beyond that point now. You're past the point where love matters. The angel took you to the precise point, the exact moment. And then the bells began to play.
It doesn't matter now; these are fixed points. These are the moments, the spaces in time, where your hearts stopped beating and the drums began. It's all you wanted. That point, that precise quiet point, flying above all that... Mess. That chaos. Where you could twist in the storm and just be loved. Be real, be the doctor. Doctor us. Be the Doctor, and rest.
But somewhere in time there's a lady, an older lady, watching a vid screen. And you're there. Little sick eyes, little secret imagination watching. All the things you'll never have; all the men you'll never be. She's talking to her daughter, who's giving her daughter in turn a little jolt, a pretty little wave, as she cries out and whispers. As she reaches out toward the screen, like she's trying to meet her -- all the way across the solar system, she'll reach for Adelaide. Her grandmother, who dies today.
She's been gone for two years; her kids are nearly over missing her, and it makes her sad. Every time she tries to say something the solar flares act up. She knows this, and that her daughter can't hear her, urging her to talk faster, talk faster, so she can hear it all before she's gone. And then she's gone.
The Doctor lands on Mars in a funny red spacesuit with a yellow helmet, wandering away from the TARDIS with a huge smile on his face. Davros said he ran, and kept running, out of shame. But it isn't shame, it's pain. Without a home to go home to, Earth is all he's got, and she keeps breaking his heart. Watch.
Yuri's joking around outside Bowie Base One while they watch him on the cameras, inside. He's wasting time, but it's just a joke: A solar panel, painted brightly with NO TRESPASSERS. It's a joke, because there's nobody here. Some of them inside are charmed but most of them are just spread too thin. "We come all this way, to an empty planet, untouched by civilization, and what do we do? Put up cheap jokes. That's not funny, that's pollution!" Ed's the reliable one; there's a whole story there, but we only see pieces of it. Adelaide comes in, a little edgy from seeing her daughter, and yells at them all, especially Ed, but after two years it's hard to take her seriously.